shell总结
1、Compound commands
| Compound commands overview | |
|---|---|
| Grouping | |
{ …; } |
command grouping |
( … ) |
command grouping in a subshell |
| Conditionals | |
[[ ... ]] |
conditional expression |
if …; then …; fi |
conditional branching |
case … esac |
pattern-based branching |
| Loops | |
for word in …; do …; done |
classic for-loop |
for ((x=1; x<=10; x++)); do ...; done |
C-style for-loop |
while …; do …; done |
while loop |
until …; do …; done |
until loop |
| Misc | |
(( ... )) |
arithmetic evaluation |
select word in …; do …; done |
user selections |
2、Expansions and substitutions
| Introduction to expansions and substitutions | |
|---|---|
{A,B,C} {A..C} |
Brace expansion |
~/ ~root/ |
Tilde expansion |
$FOO ${BAR%.mp3} |
Parameter expansion |
`command` $(command) |
Command substitution |
<(command) >(command) |
Process substitution |
$((1 + 2 + 3)) $[4 + 5 + 6] |
Arithmetic expansion |
Hello <---> Word! |
Word splitting |
/data/*-av/*.mp? |
Pathname expansion |
3、Builtin Commands
|
Declaration commands Commands that set and query attributes/types, and manipulate simple datastructures. |
Alt | Type | |
|---|---|---|---|
| declare | Display or set shell variables or functions along with attributes. |
typeset |
builtin |
| export | Display or set shell variables, also giving them the export attribute. | - | special builtin |
| eval | A common misspelling of "evil" | - | special builtin |
| local | Declare variables as having function local scope. | - | builtin |
| readonly | Mark variables or functions as read-only. |
declare -r |
special builtin |
| unset | Unset variables and functions. | - | special builtin |
| shift | Shift positional parameters | - | special builtin |
|
Control flow and data processing Commands that operate on data and/or affect control flow. |
Alt | Type | |
|---|---|---|---|
| colon | "true" null command | true | special builtin |
| dot | Source external files | source | special builtin |
| false | Fail at doing nothing | - | builtin |
| continue / break | continue with or break out of loops. | - | special builtin |
| let | Arithmetic evaluation - an old fashioned way. | - | builtin |
| return | Break out of a function, returning the specified exit status. | - | special builtin |
| [ |
The classic test command. |
test | builtin |
|
Process and Job control Commands related to jobs, signals, process groups, subshells. |
Alt | Type | |
| exec | Replace the shell, set redirections. | - | special builtin |
| exit | Exit the shell. | - | special builtin |
| trap | Set traps. | - | special builtin |
| times | Display process times. | - | special builtin |
| wait | Wait for background jobs and asynchronous lists. | - | builtin |
|
I/O Commands for reading/parsing input, or producing/formatting output of standard streams. |
Alt | Type | |
|---|---|---|---|
| coproc | Co-processes: Run a compound command in the background with async I/O. | - | keyword |
| echo | Create output from args. | - | builtin |
| mapfile | Create arrays from lines of input |
readarray |
builtin |
| printf |
"advanced echo." |
- | builtin |
| read | Build variables or arrays from input streams. | - | builtin |
|
Configuration and Debugging Commands that modify shell behavior, change special options, assist in debugging. |
Alt | Type | |
| caller | Identify/print execution frames. | - | builtin |
| set | Control positional parameters and shell behaviour. | - | special builtin |
| shopt | set/get shell options. | - | builtin |
