Set
| set -x | Display commands and their arguments as they are executed. +x turn off |
| set -v | Display shell input lines as they are read. +v turn off |
Params
| $? | error code |
| $# | a number of params |
| $@ | list params |
| $* | list params |
| $0 | script name |
| $1 | param nr 1 |
| $$ | process ID |
Keybindings
| S-M-$ | complete variable |
|---|---|
| S-< | first command in history |
| C-p | previous command in history |
| C-n | next command in history |
| S-> | last command in history |
| C-e | jump to EOL |
| C-a | jump to BOL |
| M-f | jump forward a word |
| M-b | jump back a world |
| C-u | delete from BOL to cursor |
| C-k | delete from cursor to EOL |
| M-d | delete word forward from cursor |
| C-w | delete word backward from cursor |
Variable manipulation
- (command1; command2;…) #command inside brackeds are lauched in subshell with new process id(childs)
subshell variables are recognized in subshell only
- ${var}
- ${#var} #a number of variable var characters
| command | output | desc |
|---|---|---|
| export var=(el1 el2 el3); echo ${var[1]} | val2 | the second element var variable, which is a list |
| export var=(el1 el2 el3); echo ${#var[1]} | 4 | a number of chars in the second element |
| export var=(el1 el2 el3); echo ${#var[@]} | 3 | list size |
| export var=12345; echo ${var:-text} | if var was set the output is var value, if not the output is text, var is not change | |
| export var=12345; echo ${var:=text} | if var was set the output is var value, if not the output is text, var is changed to text | |
| export var=12345; echo ${var:?text} | if var was set the output is var value, if not the output is text to the error output | |
| export var=12345; echo ${var:+text} | if var was set the output is text, var is not change | |
| export var=12345; echo ${var:1:3} | 234 | get second element (first is 0) and next 3 |
| export var=12345; echo ${var#12} | 345 | remove elements based on schema 12 from the begining |
| export var=12345; echo ${var%45} | 123 | remove elements based on schema 45 from the end |
| export var=12345; echo ${var/34/ab} | 12ab5 | substitute elements by pattern 34 to ab anywhere |
| export var=12345; echo ${var/#12/ab} | ab123 | substitute elements by pattern 12 to ab from the beggining |
| export var=12345; echo ${var/%45/ab} | 123ab | substitute elements by pattern 45 to ab from the end |
Array
- Array=(el01 el02 el03)
- element at the table is matched by [] symbol and by ${Array[0]}
- iteration: for i in ${Array[@]};do echo $i; done
Buildin variables and commands
| zmienna | desc |
|---|---|
| BASH_SUBSHELL | subshell nr |
| SECONDS | amount of time running script |
| FUNCNAME | fuction name |
| DIRSTACK | current dir |
| LINENO | currend row |
| : | true |
| PWD | current dir |
| CDPATH | cd command path |
| TMOUT | logout after [sec] of inactivity |
Debug
| bash -n [script] | set -n | check without run |
| bash -x [script] | set -x | debug |
Range variable
- function inherits variables from script
- script do not inherit variable from function
- script inherit variable from for loop
Function
- {} #anonymous function, variables from script
- in {} there is the block of code which output might be redirect to file {} > output.file,
block of code from {} is not placed in subshell like for ()
Test
[[
- less suprises, safer to use, but it is not portable, not POSIX only bash,
regexp matching, it is a keyword, not a program
- string comparision:
<, >, =, ==, !=
- integer comparison:
-lt, -le, -eq, -ge, -gt, -ne
- conditional evaluation:
&&, ||
- expression grouping:
(…)
[
- right side must be quote ex. if [ -z "$variable ], is sysnonym for test but
requires a final ], it is a program /usr/bin/[
- string comparision:
\<, \>, =, !=
- integer comparison:
-lt, -le, -eq, -ge, -gt, -ne
files
| -f file | true if file exists and is a regular file |
| -e file | true if file exists |
| -d file | true if file exists and is a directory |
strings
| -z string | true if the length of string is zero |
| -n string | true if the length of string is non-zero |
using
- [ c1 ] ||/&& [ c2 ]
- both alternatives are different ex:
c1 c2 and OK is run and FAIL is not run or OK is not run or FAIL is run
Getopts
| variable | description |
|---|---|
| OPTIND | Holds the index to the next argument to be processed. This is how getopts "remembers" its own status between invocations. Also usefull to shift the positional parameters after processing with getopts. OPTIND is initially set to 1, and needs to be re-set to 1 if you want to parse anything again with getopts |
| OPTARG | This variable is set to an argument for an option found by getopts, but if the option is unknown it contains the option flag. |
| OPTERR | (Values 0 or 1) Indicates if Bash should display error messages generated by the getopts builtin. The value is initialized to 1 on every shell startup - so be sure to always set it to 0 if you don't want to see annoying messages! |
- getopts OPTSTRING VARNAME [ARGS…]
OPTSTRING tells getopts which options to expect and where to expect arguments (see below) VARNAME tells getopts which shell-variable to use for option reporting ARGS tells getopts to parse these optional words instead of the positional parameters
- commands without any args - nothing happened? Right. getopts didn't see any valid or invalid options (letters preceeded by a dash),
so it wasn't triggered.
- commands without any flags - nothing happened? The very same case: getopts didn't see any valid or invalid options
(letters preceeded by a dash), so it wasn't triggered.
- invalid options don't stop the processing: If you want to stop the script, you have to do it yourself (exit in the right place)
- multiple identical options are possible: If you want to disallow these, you have to check manually (e.g. by setting a variable or so)
OPTSTRING
- When you want getopts to expect an argument for an option, just place a : (colon) after the proper option flag.
- If the very first character of the option-string is a : (colon), which normally would be nonsense
because there's no option letter preceeding it, getopts switches to the mode "silent error reporting".
In productive scripts, this is usually what you want (handle errors yourself and don't get disturbed by annoying messages).
ARGS
- The getopts utility parses the positional parameters of the current shell or function by default (which means it parses "$@").
You can give your own set of arguments to the utility to parse. Whenever additional arguments are given after the VARNAME parameter,
getopts doesn't try to parse the positional parameters, but these given words.
A call to getopts without these additional arguments is equivalent to explicitly calling it with "$@".
Calculate
- echo $((2+3))
Return status
- last command at function or script determe exit status, thisis bash return value
- exit status might be at range 0-255
Commands
| eval | change string from variable to command ex. i="ls"; eval $i |
| source | from command line run script, from script working as #include (same as dot-command) |
| exec | do not create fork but create new shell process, go out from script |
| true,false | return 0 as exit status of error |
| help [bash_command] | help for bash commands ex. help eval |
Output
ex 1: command > /dev/null 2>&1
- redirect standard output /dev/stdout to /dev/null
- redirect standard error /dev/stderr to device point at standard output /dev/stdout, so to /dev/null
Summarize: all output is redirect to /dev/null
ex 2: command 2>&1 > /dev/null
- redirect error output /dev/stderr to device point at standard output /dev/stdout
- redirect standard ouptut /dev/stdout to /dev/null but error output /dev/stderr
is still redirected to /dev/stdout
Summarize: /dev/stdout to /dev/null and /dev/stderror to previous /dev/stdout
Printf
- printf "%-30s%s" "hello" $VAR
Colors in directory
- dircolors -p ~/.dircolors
- eval `/usr/bin/dircolors -b ~/.dircolors`
- alias dir="dir –color"
- alias ls="ls –color"
color symbols
| desc | atrybut | |
|---|---|---|
| none | 00 | |
| bold | 01 | |
| underscore | 04 | |
| blink | 05 | |
| reverse | 07 | |
| concealed | 08 | |
| font kolor | background color | |
| black | 30 | 40 |
| red | 31 | 41 |
| green | 32 | 42 |
| yellow | 33 | 43 |
| blue | 34 | 44 |
| magenta | 35 | 45 |
| cyan | 36 | 46 |
| white | 37 | 47 |