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https://github.com/jbranchaud/til
synced 2026-01-03 23:28:02 +00:00
Change the zsh heading to unix.
This commit is contained in:
jbranchaud
@@ -1,6 +0,0 @@
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# All The Environment Variables
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If you want to see all the environment variables defined on your machine,
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you can list them all out with `printenv`. If you are like me, you probably
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have a ton of them. Pipe it through `less` to make it easier to navigate and
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search through (i.e. `printenv | less`).
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@@ -1,27 +0,0 @@
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# Cat A File With Line Numbers
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You can quickly view a file using `cat`
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```
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$ cat Gemfile
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source 'https://rubygems.org'
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# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
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gem 'rails', '4.2.0'
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# Use postgresql as the database for Active Record
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gem 'pg'
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```
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With the `-n` flag you can view that file with line numbers
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```
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$ cat -n Gemfile
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1 source 'https://rubygems.org'
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2
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3
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4 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
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5 gem 'rails', '4.2.0'
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6 # Use postgresql as the database for Active Record
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7 gem 'pg'
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```
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@@ -1,20 +0,0 @@
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# Check If A Port Is In Use
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The `lsof` command is used to *list open files*. This includes listing
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network connections. This means I can check if a particular port is in use
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and what process is using that port. For instance, I can check if my rails
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application is currently running on port 3000.
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```
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$ lsof -i TCP:3000
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COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
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ruby 13821 jbranchaud 12u IPv6 0xdf2e9fd346cc12b5 0t0 TCP localhost:hbci (LISTEN)
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ruby 13821 jbranchaud 13u IPv4 0xdf2e9fd33ca74d65 0t0 TCP localhost:hbci (LISTEN)
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```
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I can see that a ruby process (my rails app) is using port 3000. The PID
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and a number of other details are included.
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See more details with `man lsof`.
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h/t [Mike Chau](https://twitter.com/money_mikec)
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@@ -1,7 +0,0 @@
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# Clear The Screen
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If you type `clear` into your shell, the screen will be cleared. There is a
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handy keybinding though that will save you a few keystrokes. Just hit
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`ctrl-l` to achieve the same effect.
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source: [Derek P.](https://twitter.com/DerkTheDaring)
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@@ -1,23 +0,0 @@
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# Create A File Descriptor with Process Substitution
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Process substitution can be used to create a file descriptor from the
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evaluation of a shell command. The syntax for process substitution is
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`<(LIST)` where `LIST` is one or more bash commands.
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```
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$ cat <(echo 'hello, world')
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hello, world
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```
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This is particularly useful for commands that expect files, such as diff:
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```
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$ diff <(echo 'hello, world') <(echo 'hello, mars')
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1c1
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< hello, world
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---
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> hello, mars
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```
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Sources: [Brian Dunn](https://twitter.com/higgaion) and
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[Bash Guide for Beginners](http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_03_04.html#sect_03_04_07)
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@@ -1,6 +0,0 @@
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# Do Not Overwrite Existing Files
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When using the `cp` command to copy files, you can use the `-n` flag to make
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sure that you do not overwrite existing files.
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h/t [Dillon Hafer](https://twitter.com/dillonhafer)
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@@ -1,16 +0,0 @@
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# File Type Info With File
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Use the `file` utility to determine the type of a file:
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```bash
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$ file todo.md
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todo.md: ASCII English text
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$ file Hello.java
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Hello.java: ASCII C++ program text
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$ file Hello.class
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Hello.class: compiled Java class data, version 52.0
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```
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The `Hello.java` file isn't exactly a C++ program, but close enough.
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@@ -1,13 +0,0 @@
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# Find Newer Files
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Use the `-newer` flag with the name of a file to find files that have a
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newer modification date than the named file.
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For instance,
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```
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$ find blog -name '*.md' -newer blog/first-post.md
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```
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will find all markdown files in the `blog` directory that have a
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modification date more recent than `blog/first-post.md`.
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@@ -1,28 +0,0 @@
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# Global Substitution On The Previous Command
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Let's say we just executed the following command:
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```bash
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$ grep 'foo' foo.md
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```
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It gave us the information we were looking for and now we want to execute
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a similar command to find the occurrences of `bar` in `bar.md`. The `^`
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trick won't quite work here.
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```bash
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$ ^foo^bar<tab>
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$ grep 'bar' foo.md
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```
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What we need is a global replace of `foo` in our previous command. The `!!`
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command can help when we sprinkle in some `sed`-like syntax.
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```bash
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$ !!gs/foo/bar<tab>
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$ grep 'bar' bar.md
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```
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For a short command like this, we haven't gained much. However, for large
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commands that span the length of the terminal, this can definitely save us
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a little trouble.
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@@ -1,40 +0,0 @@
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# Hexdump A Compiled File
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The `hexdump` unix utility allows you to dump the contents of a
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compiled/executable file in a _readable_ hexadecimal format. Adding the `-C`
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flag includes a sidebar with a formatted version of that row of hexadecimal.
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For example, a compiled _Hello World_ java program, `Hello.java`, will look
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something like this:
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```
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> cat Hello.class | hexdump -C
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00000000 ca fe ba be 00 00 00 34 00 1d 0a 00 06 00 0f 09 |.......4........|
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00000010 00 10 00 11 08 00 12 0a 00 13 00 14 07 00 15 07 |................|
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00000020 00 16 01 00 06 3c 69 6e 69 74 3e 01 00 03 28 29 |.....<init>...()|
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00000030 56 01 00 04 43 6f 64 65 01 00 0f 4c 69 6e 65 4e |V...Code...LineN|
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00000040 75 6d 62 65 72 54 61 62 6c 65 01 00 04 6d 61 69 |umberTable...mai|
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00000050 6e 01 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 |n...([Ljava/lang|
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00000060 2f 53 74 72 69 6e 67 3b 29 56 01 00 0a 53 6f 75 |/String;)V...Sou|
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00000070 72 63 65 46 69 6c 65 01 00 0a 48 65 6c 6c 6f 2e |rceFile...Hello.|
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00000080 6a 61 76 61 0c 00 07 00 08 07 00 17 0c 00 18 00 |java............|
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00000090 19 01 00 0d 48 65 6c 6c 6f 2c 20 57 6f 72 6c 64 |....Hello, World|
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000000a0 21 07 00 1a 0c 00 1b 00 1c 01 00 05 48 65 6c 6c |!...........Hell|
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000000b0 6f 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 4f 62 |o...java/lang/Ob|
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000000c0 6a 65 63 74 01 00 10 6a 61 76 61 2f 6c 61 6e 67 |ject...java/lang|
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000000d0 2f 53 79 73 74 65 6d 01 00 03 6f 75 74 01 00 15 |/System...out...|
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000000e0 4c 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 74 |Ljava/io/PrintSt|
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000000f0 72 65 61 6d 3b 01 00 13 6a 61 76 61 2f 69 6f 2f |ream;...java/io/|
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00000100 50 72 69 6e 74 53 74 72 65 61 6d 01 00 07 70 72 |PrintStream...pr|
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00000110 69 6e 74 6c 6e 01 00 15 28 4c 6a 61 76 61 2f 6c |intln...(Ljava/l|
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00000120 61 6e 67 2f 53 74 72 69 6e 67 3b 29 56 00 20 00 |ang/String;)V. .|
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00000130 05 00 06 00 00 00 00 00 02 00 00 00 07 00 08 00 |................|
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00000140 01 00 09 00 00 00 1d 00 01 00 01 00 00 00 05 2a |...............*|
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00000150 b7 00 01 b1 00 00 00 01 00 0a 00 00 00 06 00 01 |................|
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00000160 00 00 00 01 00 09 00 0b 00 0c 00 01 00 09 00 00 |................|
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00000170 00 25 00 02 00 01 00 00 00 09 b2 00 02 12 03 b6 |.%..............|
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00000180 00 04 b1 00 00 00 01 00 0a 00 00 00 0a 00 02 00 |................|
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00000190 00 00 03 00 08 00 04 00 01 00 0d 00 00 00 02 00 |................|
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000001a0 0e |.|
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000001a1
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```
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@@ -1,14 +0,0 @@
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# Killing A Frozen SSH Session
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Whenever an SSH session freezes, I usually mash the keyboard in desperation
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and then kill the terminal session. This can be avoided though. SSH will
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listen for the following kill command:
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```
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~.<cr>
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```
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This will kill the frozen SSH session and leave you in the terminal where
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you were before you SSH'd.
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source: [Jack C.](http://hashrocket.com/team/jack-christensen)
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@@ -1,22 +0,0 @@
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# List All The Say Voices
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The `say` command can be a fun party trick.
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```bash
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$ say Get ready for the bass to drop
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```
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Your friends will be even more impressed when you use some of the alternate
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voices.
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```bash
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$ say -v Daniel Would you like a cup of tea?
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```
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To see all the alternate voices available, type the following
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```bash
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$ say -v '?'
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```
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[source](http://stackoverflow.com/questions/1489800/getting-list-of-mac-text-to-speech-voices-programmatically)
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@@ -1,10 +0,0 @@
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# Only Show The Matches
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Tools like `grep`, `ack`, and `ag` make it easy to search for lines in a
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file that contain certain text and patterns. They all come with the `-o`
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flag which tells them to only show the part that matches.
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This is particularly powerful when used with regex and piped into other
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programs.
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h/t Dillon Hafer
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@@ -1,9 +0,0 @@
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# Repeat Yourself
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Use the `repeat` command to repeat some other command.
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You can repeat a command any number of times like so
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```
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$ repeat 5 say Hello World
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```
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@@ -1,21 +0,0 @@
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# Saying Yes
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Tired of being prompted for confirmation by command-line utilities? Wish you
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could blindly respond 'yes' to whatever it is they are bugging you about?
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The `yes` command is what you've been looking for.
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```
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$ yes | rm -r ~/some/dir
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```
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This will respond `y` as `rm` asks for confirmation on removing each and
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every file in that directory.
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`yes` is just as good at saying *no*. Give it `no` as an argument and it
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will happily (and endlessly) print `no`.
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```
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$ yes no
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```
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h/t [Chris Erin](https://twitter.com/MCNormalMode)
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@@ -1,12 +0,0 @@
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# Search History
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Often times there is a very specific command you have entered into your bash
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prompt that you need to run again. You don't want to have to type it again
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and stepping manually through your history may be suboptimal if you typed it
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quite a while ago. Fortunately, there is a simple history search feature
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that you can use in this kind of situation.
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Hit `Ctrl+r` and then start typing a moderately specific search term. Your
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search history will be filtered by that term. Subsequent hitting of
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`Ctrl+r` will step forward through that filtered history. Once you find the
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command you are looking for, hit enter to execute it.
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@@ -1,11 +0,0 @@
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# Securely Remove Files
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If you really want to make sure you have wiped a file from your hard drive,
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you are going to want to use `srm` instead of `rm`. The man page for `srm`
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gives the following description:
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> srm removes each specified file by overwriting, renaming, and truncating
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> it before unlinking. This prevents other people from undeleting or
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> recovering any information about the file from the command line.
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h/t Dillon Hafer
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@@ -1,7 +0,0 @@
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# SSH With Port Forwarding
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Use the `-L` flag with `ssh` to forward a connection to a remote server
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```
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$ ssh someserver -L3000:localhost:3000
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```
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@@ -1,17 +0,0 @@
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# Switch Versions of a Brew Formula
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If you've installed a couple versions of a program via brew and you'd like
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to switch from the currently linked version to the other installed version,
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you can use the `switch` command. For instance, if you are on version
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`1.8.2` of `phantomjs` and you'd like to switch to `1.9.0`, you can simply
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invoke:
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```
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$ brew switch phantomjs 1.9.0
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```
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More generically:
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```
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$ brew switch <formula> <version>
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```
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@@ -1,15 +0,0 @@
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# Watch The Difference
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The `watch` command is a simple way to repeatedly run a particular command.
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I'll sometimes use it to monitor the response from some endpoint. `watch`
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can make monitoring responses even easier when the `-d` flag is employed.
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This flag instructs `watch` to highlight the parts of the output that are
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*different* from the previous run of the command.
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So if I run
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```
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$ watch -d curl -LIs localhost:3000
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```
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I can easily see if the http status of the request changes.
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@@ -1,16 +0,0 @@
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# Watch This Run Repeatedly
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I usually reach for a quick bash for loop when I want to run a particular
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process a bunch of times in a row. The `watch` command is another way to
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run a process repeatedly.
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```
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watch rspec spec/some/test.rb
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```
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The default is 2 seconds in between subsequent executions of the command.
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The period can be changed with the `-n` flag though:
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```
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watch -n 2 rspec spec/some/test.rb
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```
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@@ -1,21 +0,0 @@
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# Where Are The Binaries?
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When I want to know where an executable is, I use `which` like so:
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```
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$ which rails
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/Users/jbranchaud/.gem/ruby/2.1.4/bin/rails
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```
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That is the rails binary on my path that will be used if I enter a rails command.
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However, with something like rails, there may be multiple versions on your
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path. If you want to know where all of them are, you can use `where`, like
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so:
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```
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$ where rails
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/Users/jbranchaud/.gem/ruby/2.1.4/bin/rails
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/Users/jbranchaud/.rubies/2.1.4/bin/rails
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/usr/bin/rails
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```
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Reference in New Issue
Block a user