alexanderm33 / cheatsheet-shell-a4

:school: Examine your shell skills

1 Shell CheatSheet

• PDF Link: cheatsheet-shell-A4.pdf, Category: languages
• Blog URL: https://cheatsheet.dennyzhang.com/cheatsheet-shell-A4
• Related posts: Vim CheatSheet, #denny-cheatsheets

File me Issues or star this repo.

1.1 Basic

Name	Comment
Redirect stdout/stderr	ls /tmp >/dev/null 2>&1
Deal with filename	basename $f, dirname $f
Use timeout: avoid command hang	timeout 10 sh -c ‘ls -lt’
Restart shell without killing terminal	exec -l $SHELL
Run sub-shell	echo $BASH_SUBSHELL; ( echo "Running in subshell: $BASH_SUBSHELL" )
Set pipefail	set -ueoxv pipefail, set +ueoxv pipefail
Shell match regexp	=echo $str, then grep “$regexp”=
Shell match regexp	expr match "$date" "^[0-9]\{8\}" >/dev/null && echo yes
Run static code check	Link: shellcheck
Show date in utc	date -u
Check file type of a given type	file /etc/hosts
Check command type of a command	type echo

1.2 Shell script

Name	Comment
Trap exit signal	code/trap-exit.sh
Shell retry	code/shell-retry.sh
Check if a string contains a substring	code/string-contains.sh
Check if a string in a list	code/string-in-list.sh, Link: stackoverflow
Log with timestamp	code/log-with-timestamp.sh
Quit if current user is not root	code/assert-user-root.sh
Set -x on fly	code/restore-debug-output.sh
Shell run curl check	code/curl-test.sh

1.3 Environment variables

Name	Comment
List all environment variables	export
Define a new env variable	export NAME1=”value1”
Define a variable with default value of others	export MYVAR=”${MYVAR:-$OTHERVAR}”

1.4 iterm

Name	Comment
Delete a word	Ctrl+w

1.5 zsh

Name	Comment
Disable all zsh’s autocorrect	In ~/.zshrc, unsetopt correct_all
Disable a given autocorrect	In ~/.zshrc, alias ssh=’nocorrect ssh’. zsh_disable

1.6 GNU tools

1.6.1 Echo string

Name	Comment
Echo red text	echo -e “hello,\e[0;31m there \e[0;31m”
Echo multiple lines	echo -e “hello,\ndenny”
Echo bold text	echo -e hello, “\033[1mThis is bold text.\033[0m”
Echo underlined text	echo -e hello, “\033[4mThis is underlined text.\033[0m”

1.7 Shell Basic

1.7.1 cd

Name	Comment
Go to given folder	cd /var/log/
Go to folder in subshell	(cd /var/log/ && ls) After this, PWD won’t be changed
Go to home	cd
Go to parent folder	cd ..
Go to previous folder	cd -

1.7.2 Numeric

Name	Comment
*	expr 5 \* 4
+	let z=x+y, z=$x+$y
==	int1 -eq int2, =[ $? -eq 0 ] && echo “good”=
>=	int1 -ge =int2
>	int1 -gt =int2
<=	int1 -le =int2
<	int1 -lt =int2
!=	int1 -ne =int2

1.7.3 xargs

# Run grep for files filtered by find
find /var/log -name "*.log" | xargs grep -i error

# Loop with pipes
cat /etc/passwd | awk -F':' '{print $1}' | xargs -I{} sudo -l -U {} | grep -v "not allowed to"

1.8 Scripts

• Compare command output

[ 0 -eq $(find ./data -name "*.txt" -type f -print | wc -l) ]

• get ip from eth0

/sbin/ifconfig eth0 | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}'

1.9 More Resources

License: Code is licensed under MIT License.