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.
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.
Send (or "pipe") output of one command to another with |:
$ ls | wc -l
Send output to a file with >:
$ ls > files.txt
Run multiple commands with &&:
$ ls > files.txt && head files.txt
Use case: Find text.
grep stands for "global regular expression print," although you don’t have to use regex. See Rubular.com for a handy regex editor and cheat sheet.
Basic format:
$ grep [options] pattern [file or directory]
Sample greps:
# Recursive search
$ grep -r 'title' content
# Match beginning of line with ^
$ grep -r '^title: ' content
# Use -l to only show filenames in output
$ grep -lr '^title: ' content
# Use -h to only show matched lines in output
$ grep -hr '^title: ' content
# Pipe results to another grep
$ grep -r '^title: ' content | grep '{'
$ grep -r '^intro: ' content
# Use -L to show non-matching filenames
$ grep -Lr '^intro' content
# Use -v to exclude lines that match the pattern
$ grep -Lr '^intro' content | grep -v index.md | grep -v README
# Use egrep for more regex support
$ grep -Lr '^intro' content | egrep -v '(index|README).md'
Use case: Find files.
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.
Basic format:
$ find [directory] [option] pattern
Sample finds:
$ find content -name 'about-actions.md'
$ find . -name 'about-actions.md'
$ find data -name '*.yml'
$ find content -type f
$ find translations -type f | wc -l
$ find content -type d
$ find content/actions -type d | grep getting-started
Use case: Do something to each item in a collection.
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.
Basic format:
$ for var in list; do [commands]; done
Sample for loops:
$ for i in $(ls content); do echo $i; done
$ for i in $(ls translations | grep -v README); do git mv translations/$i/content/foo.md translations/$i/content/bar.md; done
$ for i in {1..50}; do mkdir problem-${i}; done
$ for i in {1..5}; do expr $i + 5; done
$ for v in 2.19 2.18 2.17 2.16; do script/enterprise-backport $v; done
$ 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
Use case: Find and replace.
sed is one way to do find/replace on the command line.
Basic format:
$ sed 's/pattern/replacement/[flags]'
The / is the most common delimiter, but other characters work too:
$ sed 's_pattern_replacement_[flags]'
Sample seds:
# Do a substitution on standard output
$ grep -hr 'title: ' content | sed 's/title: //g' | sort
# Send results to file
$ grep -hr 'title: ' content | sed 's/title: //g' | sort > titles.txt
# Find duplicate titles
$ grep --exclude='README.md' -rh '^title: ' content | sed 's/title: //g' | sort | uniq -d
# Do an in-place substitution on a file
$ sed -i '' s'/Help Docs/docs.github.com/g' README.md