源自：https://devhints.io/bash
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Go to previous directory
cd -
Subshells
(cd somedir; echo "I'm now in $PWD")
pwd # still in first directory
Conditionals execution
git commit && git push
git commit || echo "commit failed"
Conditionals
if [ -z "$string" ]; then
echo "empty"
elif [ -n "$string" ]; then
echo "not empty"
Function arguments
$# Number of arguments
$* All arguments
$@ All arguments, starting from first
$1 First argument
}
echo "You are $(get_name)"
Function return values
get_name() {
echo "John" # return
}
echo "You are $(get_name)"
Brace expansion
echo {a,b}.js
echo {a..z}.js
String quotes
NAME="Hohn"
echo "Hi $NAME"
echo 'Hi $NAME'
Shell execution
echo "I'm in $(pwd)"
echo "I'm in `pwd`"
Length
${#FOO} Length of $FOO
Default values
${FOO:-val} $FOO, or val if not set
${FOO:=val} Set $FOO to val if not set
${FOO:+val} val if $FOO is set
${FOO:?message} Show error message and exit if $FOO is not set
Loops
for i in /etc/rc.*; do
echo $i
done
Printf
printf "Hello %s, I'm %s" Sven Olga
#=> "Hello Sven, I'm Olga
Special variables
$? Exit status of last task
$! PID of last background task
$$ PID of shell
File conditions
[ -e FILE ] Exists
[ -r FILE ] Readable
[ -h FILE ] Symlink
[ -d FILE ] Directory
[ -w FILE ] Writable
[ -s FILE ] Size is > 0 bytes
[ -f FILE ] File
[ -x FILE ] Executable
Defining arrays
Fruits=('Apple' 'Banana' 'Orange')
Fruits[0]="Apple"
Fruits[1]="Banana"
Fruits[2]="Orange"
echo ${Fruits[0]} # Element #0
echo ${Fruits[@]} # All elements, space-separated
echo ${#Fruits[@]} # Number of elements
echo ${#Fruits} # String length of the 1st element
echo ${#Fruits[3]} # String length of the Nth element
echo ${Fruits[@]:3:2} # Range (from position 3, length 2)
for i in "${arrayName[@]}"; do
echo $i
done
