- Selection Of My Shell Scripts I Find Often Help With Several Tasks. This is the stuff I use often and I know it saves me time so I am offering whatever I make here for Every One So...
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Bash Shell Examples And Help
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Variables
NAME="John"
echo $NAME
echo "$NAME"
echo "${NAME}!"- String Quotes
NAME="John"
echo "Hi $NAME" #=> Hi John
echo 'Hi $NAME' #=> Hi $NAME- Shell Execution
echo "I'm in $(pwd)"
echo "I'm in `pwd`"- Conditional Execution
git commit && git push
git commit || echo "Commit failed"- Functions
get_name() {
echo "John"
}
echo "You are $(get_name)"- Conditionals
if [ -z "$string" ]; then
echo "String is empty"
elif [ -n "$string" ]; then
echo "String is not empty"
fi- Bash Strict Mode
set -euo pipefail
IFS=$'\n\t'- Brace Expansion
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- Parameter Expansions
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"
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)- Substitution
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- Substrings
${FOO:0:3} Substring (position, length)
${FOO:-3:3} Substring from the right- 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 The : is optional (eg, ${FOO=word} works)- Loops
for i in /etc/rc.*; do
echo $i
done- Ranges
for i in {1..5}; do
echo "Welcome $i"
done- With Step Size
for i in {5..50..5}; do
echo "Welcome $i"
done- Reading Lines
cat file.txt | while read line; do
echo $line
done- While Loops
while true; do
cmd
done- Functions
myfunc() {
echo "hello $1"
}
function myfunc() {
echo "hello $1"
}
myfunc "Sam"- Returning Values
myfunc() {
local myresult='some value'
echo $myresult
}
result=$(myfunc)- Raising Errors
myfunc() {
return 1
}
if myfunc; then
echo "success"
else
echo "failure"
fi- Arguments
$# # Number of arguments
$* # All arguments
$@ # All arguments, starting from first
$1 # First argument- Conditionals
[ -z STRING ] # Empty string
[ -n STRING ] # Not empty string
[ NUM -eq NUM ] # Equal
[ NUM -ne NUM ] # Not equal
[ NUM -lt NUM ] # Less than
[ NUM -le NUM ] # Less than or equal
[ NUM -gt NUM ] # Greater than
[ NUM -ge NUM ] # Greater than or equal
[[ STRING =~ STRING ]] # Regexp
(( NUM < NUM )) # Numeric conditions
[ -o noclobber ] # If OPTIONNAME is enabled
[ ! EXPR ] # Not
[ X ] && [ Y ] # And
[ X ] || [ Y ] # Or- File conditions
[ -e FILE ] # Exists
[ -r FILE ] # Readable
[ -h FILE ] # Symlink
[ -d FILE ] # Directory
[ -w FILE ] # Writable
[ -s FILE ] # Size is > 0 bytes
[ -f FILE ] # File
[ -x FILE ] # Executable
[ FILE1 -nt FILE2 ] # 1 is more recent than 2
[ FILE1 -ot FILE2 ] # 2 is more recent than 1
[ FILE1 -ef FILE2 ] # Same files- Example
#### String
if [ -z "$string" ]; then
echo "String is empty"
elif [ -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- Arrays
Fruits=('Apple' 'Banana' 'Orange')
Fruits[0]="Apple"
Fruits[1]="Banana"
Fruits[2]="Orange"- Working With Arrays
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 ${Fruits[@]:3:2} # Range (from position 3, length 2)
- Array Operations
```sh
Fruits=("${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- Array Iteration
for i in "${arrayName[@]}"; do
echo $i
done- Options
set -o noclobber # Avoid overlay files (echo "hi" > foo)
set -o errexit # Used to exit upon error, avoiding cascading errors
set -o pipefail # Unveils hidden failures
set -o nounset # Exposes unset variables- Glob Options
set -o nullglob # Non-matching globs are removed ('*.foo' => '')
set -o failglob # Non-matching globs throw errors
set -o nocaseglob # Case insensitive globs
set -o globdots # Wildcards match dotfiles ("*.sh" => ".foo.sh")
set -o globstar # Allow ** for recursive matches ('lib/**/*.rb' => 'lib/a/b/c.rb')
# N.B. Set GLOBIGNORE as a colon-separated list of patterns to be removed from glob matches.- History
history # Show history
shopt -s histverify # Don’t execute expanded result immediately- Expansions
!$ # Expand last parameter of most recent command
!* # Expand all parameters of most recent command
!-n # Expand nth most recent command
!n # Expand nth command in history
!<command> # Expand most recent invocation of command <command>- Operations
!!:s/<FROM>/<TO>/ # Replace first occurrence of <FROM> to <TO> in most recent command
!!:gs/<FROM>/<TO>/ # Replace all occurrences 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 !$ # Replaced with any valid expansion.- Slices
!!:n # Expand only nth token from most recent command (command is 0; first param is 1)
!!:n-m # Expand range of tokens from most recent command
!!:n-$ # Expand nth token to last from most recent command
# !! can be replaced with any valid expansion i.e. !cat, !-2, !42, etc.- Miscellaneous -- Numeric calculations
$((a + 200)) # Add 200 to $a
$((RANDOM%=200)) # Random number 0..200- Subshells
(cd somedir; echo "I'm now in $PWD")
pwd # still in first directory- Redirection
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- Traps
trap 'echo Error at about $LINENO' ERRor
traperr() {
echo "ERROR: ${BASH_SOURCE[1]} at about ${BASH_LINENO[0]}"
}
set -o errtrace
trap traperr ERR- Case / switch
case "$1" in
start | up)
vagrant up
;;
*)
echo "Usage: $0 {start|stop|ssh}"
;;
esac- Source Relative
source "${0%/*}/../share/foo.sh"
printf
printf "Hello %s, I'm %s" Sven Olga#=> "Hello Sven, I'm Olga- Directory Of Script
DIR="${0%/*}"- Getting Options
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- Heredoc
cat <<END
hello world
END
``
- Reading Input
```sh
echo -n "Proceed? [y/n]: "
read ans
echo $ans
read -n 1 ans # Just one character- Special Variables
$? Exit status of last task
$! PID of last background task
$$ PID of shell