Basics
name="John"
echo "${name}"
echo "${name/J/j}" #=> "john" (substitution)
echo "${name:0:2}" #=> "Jo" (slicing)
echo "${name::2}" #=> "Jo" (slicing)
echo "${name::-1}" #=> "Joh" (slicing)
echo "${name:(-1)}" #=> "n" (slicing from right)
echo "${name:(-2):1}" #=> "h" (slicing from right)
echo "${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 "${str%/*}" # /path/to
echo "${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=${src##*/} #=> "foo.cpp" (basepath)
dir=${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 |
: '
This is a
multi line
comment
'
Substrings
| Expression |
Description |
${foo:0:3} |
Substring (position, length) |
${foo:(-3):3} |
Substring from the right |
Length
| Expression |
Description |
${#foo} |
Length of $foo |
Manipulation
str="HELLO WORLD!"
echo "${str,}" #=> "hELLO WORLD!" (lowercase 1st letter)
echo "${str,,}" #=> "hello world!" (all lowercase)
str="hello world!"
echo "${str^}" #=> "Hello world!" (uppercase 1st letter)
echo "${str^^}" #=> "HELLO WORLD!" (all uppercase)
| Command option |
Description |
-c |
Operations apply to characters not in the given set |
-d |
Delete characters |
-s |
Replaces repeated characters with single occurrence |
-t |
Truncates |
[:upper:] |
All upper case letters |
[:lower:] |
All lower case letters |
[:digit:] |
All digits |
[:space:] |
All whitespace |
[:alpha:] |
All letters |
[:alnum:] |
All letters and digits |
Example
echo "Welcome To Devhints" | tr '[:lower:]' '[:upper:]'
WELCOME TO DEVHINTS
Directory of script
Default values
| Expression |
Description |
${foo:-val} |
$foo, or val if unset (or null) |
${foo:=val} |
Set $foo to val if unset (or null) |
${foo:+val} |
val if $foo is set (and not null) |
${foo:?message} |
Show error message and exit if $foo is unset (or null) |
Omitting the : removes the (non)nullity checks, e.g. ${foo-val} expands to val if unset otherwise $foo.
Special variables
| Expression |
Description |
$? |
Exit status of last task |
$! |
PID of last background task |
$$ |
PID of shell |
$0 |
Filename of the shell script |
$_ |
Last argument of the previous command |
${PIPESTATUS[n]} |
return value of piped commands (array) |
See Special parameters.
Numeric calculations
$((a + 200)) # Add 200 to $a
$(($RANDOM%200)) # Random number 0..199
