有用的 BASH 代码片段
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原文地址: http://stackoverflow.com/questions/965663/
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Useful BASH code snippets
提问by Nate Kohl
回答by Nate Kohl
There's cd -to go to the previously-visited directory:
有cd -去以前访问过的目录：
/usr/local/bin> cd /i/am/a/banana
/i/am/a/banana> cd -
/usr/local/bin>
...and then there are all those useful incarnations of the BASH for-loop:
...然后是 BASH for 循环的所有这些有用的化身：
for file in *.txt; do ls $file; done
for item in $(echo foo bar baz); do echo $item; done
for num in {0..9}; do echo $num; done
回答by Robert Gowland
In a BASH script, assign an argument to variable but provide a default if it exists:
在 BASH 脚本中，为变量分配一个参数，但如果存在则提供默认值：
MYVAR=${1:-default}
$MYVAR will contain the first argument if one was given else "default".
如果给定其他参数，则 $MYVAR 将包含第一个参数。
回答by Rob Wells
G'day,
G'day,
My favourite, and it's applicable to other shells that support aliases, is the simple way of temporarily disabling an alias by prepending a backslash to a command.
我最喜欢的是，它适用于支持别名的其他 shell，是通过在命令前添加反斜杠来临时禁用别名的简单方法。
So:
所以：
alias rm='rm -i'
would always give you interactive mode when entering rm, entering
输入rm时总是会给你交互模式，输入
\rm
on the command line bypasses the alias.
在命令行上绕过别名。
HTH
HTH
cheers,
干杯，
回答by Fernando Martin
回答by Fernando Martin
Found this somewhere on the net a long time ago:
很久以前在网上的某个地方发现了这个：
function bashtips {
cat <<EOF
DIRECTORIES
-----------
~- Previous working directory
pushd tmp Push tmp && cd tmp
popd Pop && cd
GLOBBING AND OUTPUT SUBSTITUTION
--------------------------------
ls a[b-dx]e Globs abe, ace, ade, axe
ls a{c,bl}e Globs ace, able
$(ls) \`ls\` (but nestable!)
HISTORY MANIPULATION
--------------------
!! Last command
!?foo Last command containing \`foo'
^foo^bar^ Last command containing \`foo', but substitute \`bar'
!!:0 Last command word
!!:^ Last command's first argument
!$ Last command's last argument
!!:* Last command's arguments
!!:x-y Arguments x to y of last command
C-s search forwards in history
C-r search backwards in history
LINE EDITING
------------
M-d kill to end of word
C-w kill to beginning of word
C-k kill to end of line
C-u kill to beginning of line
M-r revert all modifications to current line
C-] search forwards in line
M-C-] search backwards in line
C-t transpose characters
M-t transpose words
M-u uppercase word
M-l lowercase word
M-c capitalize word
COMPLETION
----------
M-/ complete filename
M-~ complete user name
M-@ complete host name
M-$ complete variable name
M-! complete command name
M-^ complete history
EOF
}
回答by Paused until further notice.
Add a space (or other delimiter) only if a variable is set, in order to avoid ugly unnecessary spaces.
仅当设置了变量时才添加空格（或其他分隔符），以避免丑陋的不必要的空格。
$ first=Joe
$ last= # last name blank, the following echoes a space before the period
$ echo "Hello, $first $last. Welcome to..."
Hello, Joe . Welcome to...
$ echo "Hello, $first${last:+ $last}. Welcome to..."
Hello, Joe. Welcome to...
$ last=Green
$ echo "Hello, $first${last:+ $last}. Welcome to..."
Hello, Joe Green. Welcome to...
回答by Paused until further notice.
To remove .svn directories you may also use the combination 'find...-prune...-exec...' (without xargs):
要删除 .svn 目录，您还可以使用组合“find...-prune...-exec...”（不带 xargs）：
# tested on Mac OS X
find -x -E . \( -type d -regex '.*/\.svn/*.*' -prune \) -ls # test
find -x -E . \( -type d -regex '.*/\.svn/*.*' -prune \) -exec /bin/rm -PRfv '{}' \;
回答by Paused until further notice.
Here is a nice grepexpression to remove blank lines and comment lines:
这是一个grep删除空行和注释行的好表达式：
grep -v '^[ \t]*$\|^[ \t]*#' /etc/ssh/sshd_config
The above will display the used settings in sshd_configwithout any clutter.
以上将在sshd_config没有任何混乱的情况下显示使用的设置。
回答by Paused until further notice.
Here is another one:
这是另一个：
#!/bin/bash
# Shows the full path of files, good for copy pasting and for when
# listing the full paths is necessary.
# Usage: Run in the working directory (no path), otherwise takes the
# same file specification as ls.
for file in $(ls "$@"); do
echo -n $(pwd)
[[ $(pwd) != "/" ]] && echo -n /
echo $file
done
回答by amarillion
At the beginning of a script that must be run as root:
在必须以 root 身份运行的脚本的开头：
if [ `id -u` != 0 ]; then
echo "This script must be run as root" 1>&2
exit 1
fi
