title | category | layout | tags | updated | keywords | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Bash scripting |
CLI |
2017/sheet |
|
2017-08-26 |
|
{: .-three-column}
#!/usr/bin/env bash
NAME="John"
echo "Hello $NAME!"
NAME="John"
echo $NAME
echo "$NAME"
echo "${NAME}!"
NAME="John"
echo "Hi $NAME" #=> Hi John
echo 'Hi $NAME' #=> Hi $NAME
echo "I'm in $(pwd)"
echo "I'm in `pwd`"
# Same
git commit && git push
git commit || echo "Commit failed"
{: id='functions-example'}
get_name() {
echo "John"
}
echo "You are $(get_name)"
See: Functions
{: id='conditionals-example'}
if [ -z "$string" ]; then
echo "String is empty"
elsif [ -n "$string" ]; then
echo "String is not empty"
fi
See: Conditionals
set -euo pipefail
IFS=$'\n\t'
See: Unofficial bash strict mode
echo {A,B}.js
| {A,B}
| Same as A B
|
| {A,B}.js
| Same as A.js B.js
|
| {1..5}
| Same as 1 2 3 4 5
|
See: Brace expansion
{: .-three-column}
name="John"
echo ${name}
echo ${name/J/j} #=> "john" (substitution)
echo ${name:0:2} #=> "jo" (slicing)
echo ${food:-Cake} #=> $food or "Cake"
length=2
echo ${name:0:length} #=> "jo"
See: Parameter expansion
STR="/path/to/foo.cpp"
echo ${STR%.cpp} # /path/to/foo
echo ${STR%.cpp}.o # /path/to/foo.o
echo ${STR##*.} # cpp (extension)
echo ${STR##*/} # foo.cpp (basepath)
echo ${STR#*/} # path/to/foo.cpp
echo ${STR##*/} # foo.cpp
echo ${STR/foo/bar} # /path/to/bar.cpp
STR="Hello world"
echo ${STR:6:5} # "world"
echo ${STR:-5:5} # "world"
SRC="/path/to/foo.cpp"
BASE=${STR##*/} #=> "foo.cpp" (basepath)
DIR=${SRC%$BASE} #=> "/path/to" (dirpath)
Code | Description |
---|---|
${FOO%suffix} |
Remove suffix |
${FOO#prefix} |
Remove prefix |
--- | --- |
${FOO%%suffix} |
Remove long suffix |
${FOO##prefix} |
Remove long prefix |
--- | --- |
${FOO/from/to} |
Replace first match |
${FOO//from/to} |
Replace all |
--- | --- |
${FOO/%from/to} |
Replace suffix |
${FOO/#from/to} |
Replace prefix |
| ${FOO:0:3}
| Substring (position, length) |
| ${FOO:-3:3}
| Substring from the right |
| ${#FOO}
| Length of $FOO
|
| ${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 |
The :
is optional (eg, ${FOO=word}
works)
{: .-three-column}
for i in /etc/rc.*; do
echo $i
done
for i in {1..5}; do
echo "Welcome $i"
done
cat file.txt | while read line; do
echo $line
done
while true; do
···
done
{: .-three-column}
myfunc() {
echo "hello $1"
}
# Same as above (alternate syntax)
function myfunc() {
echo "hello $1"
}
myfunc "John"
myfunc() {
local myresult='some value'
echo $myresult
}
result=$(myfunc)
myfunc() {
return 1
}
if myfunc; then
echo "success"
else
echo "failure"
fi
Expression | Description |
---|---|
$# |
Number of arguments |
$* |
All arguments |
$@ |
All arguments, starting from first |
$1 |
First argument |
See Special parameters.
{: .-three-column}
Condition | Description |
---|---|
[ -z STRING ] |
Empty string |
[ -n STRING ] |
Not empty string |
--- | --- |
[ NUM -eq NUM ] |
Equal |
[ NUM -ne NUM ] |
Not equal |
[ NUM -lt NUM ] |
Less than |
[ NUM -le NUM ] |
Less than or equal |
[ NUM -gt NUM ] |
Greater than |
[ NUM -ge NUM ] |
Greater than or equal |
--- | --- |
[[ STRING =~ STRING ]] |
Regexp |
--- | --- |
(( NUM < NUM )) |
Numeric conditions |
Condition | Description |
---|---|
[ -o noclobber ] |
If OPTIONNAME is enabled |
--- | --- |
[ ! EXPR ] |
Not |
[ X ] && [ Y ] |
And |
`[ X ] |
Condition | Description |
---|---|
[ -e FILE ] |
Exists |
[ -r FILE ] |
Readable |
[ -h FILE ] |
Symlink |
[ -d FILE ] |
Directory |
[ -w FILE ] |
Writable |
[ -s FILE ] |
Size is > 0 bytes |
[ -f FILE ] |
File |
[ -x FILE ] |
Executable |
--- | --- |
[ FILE1 -nt FILE2 ] |
1 is more recent than 2 |
[ FILE1 -ot FILE2 ] |
2 is more recent than 1 |
[ FILE1 -ef FILE2 ] |
Same files |
# String
if [ -z "$string" ]; then
echo "String is empty"
elsif [ -n "$string" ]; then
echo "String is not empty"
fi
# Combinations
if [ X ] && [ Y ]; then
...
fi
# Regex
if [[ "A" =~ "." ]]
if (( $a < $b ))
if [ -e "file.txt" ]; then
echo "file exists"
fi
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 ${Fruits[@]:3:2} # Range (from position 3, length 2)
Fruits=("${Fruits[@]}" "Watermelon") # Push
Fruits=( ${Fruits[@]/Ap*/} ) # Remove by regex match
unset Fruits[2] # Remove one item
Fruits=("${Fruits[@]}") # Duplicate
Fruits=("${Fruits[@]}" "${Veggies[@]}") # Concatenate
lines=(`cat "logfile"`) # Read from file
for i in "${arrayName[@]}"; do
echo $i
done
set -o noclobber # Avoid overlay files (echo "hi" > foo)
set -o errexit # Used to exit upon error, avoiding cascading errors
set -o pipefail # Unveils hidden failures
set -o nounset # Exposes unset variables
set -o nullglob # Non-matching globs are removed ('*.foo' => '')
set -o failglob # Non-matching globs throw errors
set -o nocaseglob # Case insensitive globs
set -o globdots # Wildcards match dotfiles ("*.sh" => ".foo.sh")
set -o globstar # Allow ** for recursive matches ('lib/**/*.rb' => 'lib/a/b/c.rb')
Set GLOBIGNORE
as a colon-separated list of patterns to be removed from glob
matches.
| history
| Show history |
| shopt -s histverify
| Don't execute expanded result immediately |
| !$
| Expand last parameter of most recent command |
| !*
| Expand all parameters of most recent command |
| !-n
| Expand n
th most recent command |
| !n
| Expand n
th command in history |
| !<command>
| Expand most recent invocation of command <command>
|
| !!:s/<FROM>/<TO>/
| Replace first occurence of <FROM>
to <TO>
in most recent command |
| !!:gs/<FROM>/<TO>/
| Replace all occurences of <FROM>
to <TO>
in most recent command |
| !$:t
| Expand only basename from last parameter of most recent command |
| !$:h
| Expand only directory from last parameter of most recent command |
!!
and !$
can be replaced with any valid expansion.
| !!:n
| Expand only n
th token from most recent command (command is 0
; first param is 1
) |
| !!:n-m
| Expand range of tokens from most recent command |
| !!:n-$
| Expand n
th token to last from most recent command |
!!
can be replaced with any valid expansion i.e. !cat
, !-2
, !42
, etc.
$((a + 200)) # Add 200 to $a
$((RANDOM%=200)) # Random number 0..200
(cd somedir; echo "I'm now in $PWD")
pwd # still in first directory
python hello.py > output.txt # stdout to (file)
python hello.py >> output.txt # stdout to (file), append
python hello.py 2> error.log # stderr to (file)
python hello.py 2>&1 # stderr to stdout
python hello.py 2>/dev/null # stderr to (null)
python hello.py < foo.txt
command -V cd
#=> "cd is a function/alias/whatever"
trap 'echo Error at about $LINENO' ERR
or
traperr() {
echo "ERROR: ${BASH_SOURCE[1]} at about ${BASH_LINENO[0]}"
}
set -o errtrace
trap traperr ERR
case "$1" in
start | up)
vagrant up
;;
*)
echo "Usage: $0 {start|stop|ssh}"
;;
esac
source "${0%/*}/../share/foo.sh"
printf "Hello %s, I'm %s" Sven Olga
#=> "Hello Sven, I'm Olga
DIR="${0%/*}"
while [[ "$1" =~ ^- && ! "$1" == "--" ]]; do case $1 in
-V | --version )
echo $version
exit
;;
-s | --string )
shift; string=$1
;;
-f | --flag )
flag=1
;;
esac; shift; done
if [[ "$1" == '--' ]]; then shift; fi
cat <<END
hello world
END
echo -n "Proceed? [y/n]: "
read ans
echo $ans
read -n 1 ans # Just one character
| $?
| PID of last foreground task |
| $!
| PID of last background task |
| $$
| PID of shell |
See Special parameters.
{: .-one-column}
- Bash-hackers wiki (bash-hackers.org)
- Shell vars (bash-hackers.org)
- Learn bash in y minutes (learnxinyminutes.com)