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155 lines
3.8 KiB
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155 lines
3.8 KiB
Markdown
# Sample Unix commands
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Here are some native commands available when you work in a Unix terminal (or a Bash emulator). These commands are useful when you have a task in front of you that's suited to a fast, oneoff solution.
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## Table of contents
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* [Redirecting output](#redirecting-output)
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* [`grep`](#grep)
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* [`find`](#find)
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* [`for` loops](#for-loops)
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* [`sed`](#sed)
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## Redirecting output
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When you type commands in the terminal, that’s **standard input**. When you run the command, the results typically go to **standard output**. This input/output model allows you to chain commands together to build custom one-liners.
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Send (or "pipe") output of one command to another with `|`:
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```
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$ ls | wc -l
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```
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Send output to a file with `>`:
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```
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$ ls > files.txt
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```
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Run multiple commands with `&&`:
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```
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$ ls > files.txt && head files.txt
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```
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## grep
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**Use case**: Find text.
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`grep` stands for "global regular expression print," although you don’t have to use regex. See [Rubular.com](https://rubular.com/) for a handy regex editor and cheat sheet.
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Basic format:
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```
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$ grep [options] pattern [file or directory]
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```
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Sample `grep`s:
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```
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# Recursive search
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$ grep -r 'title' content
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# Match beginning of line with ^
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$ grep -r '^title: ' content
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# Use -l to only show filenames in output
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$ grep -lr '^title: ' content
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# Use -h to only show matched lines in output
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$ grep -hr '^title: ' content
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# Pipe results to another grep
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$ grep -r '^title: ' content | grep '{'
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$ grep -r '^intro: ' content
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# Use -L to show non-matching filenames
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$ grep -Lr '^intro' content
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# Use -v to exclude lines that match the pattern
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$ grep -Lr '^intro' content | grep -v index.md | grep -v README
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# Use egrep for more regex support
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$ grep -Lr '^intro' content | egrep -v '(index|README).md'
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```
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## find
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**Use case**: Find files.
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`find` is helpful for finding files, whereas `grep` is more useful for matching patterns. `find` is recursive by default. You can pass `find` a `-depth` flag to limit recursion.
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Basic format:
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```
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$ find [directory] [option] pattern
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```
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Sample `find`s:
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```
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$ find content -name 'about-actions.md'
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$ find . -name 'about-actions.md'
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$ find data -name '*.yml'
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$ find content -type f
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$ find translations -type f | wc -l
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$ find content -type d
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$ find content/actions -type d | grep getting-started
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```
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## for loops
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**Use case**: Do something to each item in a collection.
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Every programming language has a way to iterate through a list. The following examples show the Unix shell syntax. The semicolons can be hard to read, but they make it possible to run these commands on a single line.
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Basic format:
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```
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$ for var in list; do [commands]; done
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```
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Sample `for` loops:
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```
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$ for i in $(ls content); do echo $i; done
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$ for i in $(ls translations | grep -v README); do git mv translations/$i/content/foo.md translations/$i/content/bar.md; done
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$ for i in {1..50}; do mkdir problem-${i}; done
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$ for i in {1..5}; do expr $i + 5; done
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$ for v in 2.19 2.18 2.17 2.16; do script/enterprise-backport $v; done
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$ for i in $(cat prs.txt); do curl -su <username>:$token -X "GET" "https://api.github.com/repos/github/docs-internal/pulls/${i}" | jq '. | {number: .number, state: .state}'; done
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```
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## sed
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**Use case**: Find and replace.
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`sed` is one way to do find/replace on the command line.
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Basic format:
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```
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$ sed 's/pattern/replacement/[flags]'
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```
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The `/` is the most common delimiter, but other characters work too:
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```
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$ sed 's_pattern_replacement_[flags]'
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```
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Sample `sed`s:
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```
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# Do a substitution on standard output
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$ grep -hr 'title: ' content | sed 's/title: //g' | sort
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# Send results to file
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$ grep -hr 'title: ' content | sed 's/title: //g' | sort > titles.txt
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# Find duplicate titles
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$ grep --exclude='README.md' -rh '^title: ' content | sed 's/title: //g' | sort | uniq -d
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# Do an in-place substitution on a file
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$ sed -i '' s'/Help Docs/docs.github.com/g' README.md
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```
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