xargs [-0prtx] [-E eof-str] [-e[eof-str]] [--eof[=eof-str]] [--null]
[-d delimiter] [--delimiter delimiter] [-I replace-str] [-i[replace-
str]] [--replace[=replace-str]] [-l[max-lines]] [-L max-lines]
[--max-lines[=max-lines]] [-n max-args] [--max-args=max-args] [-s max-
chars] [--max-chars=max-chars] [-P max-procs] [--max-procs=max-procs]
[--interactive] [--verbose] [--exit] [--no-run-if-empty]
[--arg-file=file] [--show-limits] [--version] [--help] [command
[initial-arguments]]
最经典应用模式： somecommand |xargs -item command
不带command ，默认的使用echo 输出
用途：
1.构造参数列表并运行命令，即将接收的参数传递给后面的command 命令执行
2.将多行输入转换为单行 （特殊功效）
优点：
1. 将输入参数整理后，去除<newline>换行符，以一个列表形式处理
2. 避免参数过长引发的问题，使用xargs -n 参数适当控制，对于经常产生大量输出的命令如find、locate和grep来说非常有用
XARGS 一般是和管道一起使用：
XXcomand | xargs -x comand initial-args
-x 代表选项
选项：
-p 操作具有可交互性，每次执行comand都交互式提示用户选择
-i -i 选项告诉 xargs 可以使用{}代替传递过来的参数， 建议使用-I，其符合POSIX标准
-I
格式： xargs -I rep-str comand
rep-srt rep-str 为代替传递给xargs参数， 可以使 {} $ @ 等符号 ，其主要作用是当xargs
command 后有多个参数时，调整参数位置。例如：
find . -name "*.txt " |xargs -I {} cp {} /tmp
-t 启用命令行输出模式：其先回显要运行的命令，然后执行命令，打印出命令结果，跟踪与调试xargs的利器，也是研究xargs运行原理的好办法；
-r
如果没有要处理的参数传递给xargsxargs 默认是带 空参数运行一次，如果你希望无参数时，停止 xargs，直接退出，使用 -r
选项即可，其可以防止xargs 后面命令带空参数运行报错。If the standard input does not contain any
nonblanks, do not run the command, exit
-s size
设置每次构造Command行的长度总大小,包括 command +init-param +传递参数,Size 参数必须是正整数
-L num
从标准输入一次读取num行送给Command命令 ，-l和-L功能一样，不建议使用。
-n
xargs 的-n选项设置每次送给command命令的参数个数，参数以空白字符或<newline>换行符分割
-L 和 -n 标志是互相排斥的；最后指定的标志生效。
-x 如果有任何 Command 行大于 -s Size 标志指定的字节数，停止运行 xargs 命令，-L -I -n 默认打开-x参数
常见的经典用法：
find . -name "*.txt" |xargs rm {}
帮助理解各个参数的实例
-t 参数，打开调试功能，显示每次所组的命令，在调试中非常有用，可以看出xargs的执行原理
-L num 参数控制每次输入的行数，如下是控制每次输入2行
- [[email protected] ~/tmp/dir]#ls -l
- total 44
- -rwx------ 1 root root 1026 Sep 27 05:28 data.txt
- -rw-r--r-- 1 root root 1047 Sep 27 05:28 d.txt
- -rwx------ 1 root root 2009 Sep 27 05:28 env2.txt
- -rwx------ 1 root root 2009 Sep 27 05:28 env.txt
- -rwx------ 1 root root 1998 Sep 27 05:28 export2.txt
- -rwx------ 1 root root 1998 Sep 27 05:28 export.txt
- -rwx------ 1 root root 28 Sep 27 05:28 fuck.txt
- -rwx------ 1 root root 5373 Sep 27 05:28 set.txt
- -rw-r--r-- 1 root root 21 Sep 27 05:28 s.txt
- -rw-r--r-- 1 root root 35 Sep 27 10:13 t.txt
- [[email protected] ~/tmp/dir]#ls -l |xargs -t -L 2
- /bin/echo total 44 -rwx------ 1 root root 1026 Sep 27 05:28 data.txt
- total 44 -rwx------ 1 root root 1026 Sep 27 05:28 data.txt
- /bin/echo -rw-r--r-- 1 root root 1047 Sep 27 05:28 d.txt -rwx------ 1 root root 2009 Sep 27 05:28 env2.txt
- -rw-r--r-- 1 root root 1047 Sep 27 05:28 d.txt -rwx------ 1 root root 2009 Sep 27 05:28 env2.txt
- /bin/echo -rwx------ 1 root root 2009 Sep 27 05:28 env.txt -rwx------ 1 root root 1998 Sep 27 05:28 export2.txt
- -rwx------ 1 root root 2009 Sep 27 05:28 env.txt -rwx------ 1 root root 1998 Sep 27 05:28 export2.txt
- /bin/echo -rwx------ 1 root root 1998 Sep 27 05:28 export.txt -rwx------ 1 root root 28 Sep 27 05:28 fuck.txt
- -rwx------ 1 root root 1998 Sep 27 05:28 export.txt -rwx------ 1 root root 28 Sep 27 05:28 fuck.txt
- /bin/echo -rwx------ 1 root root 5373 Sep 27 05:28 set.txt -rw-r--r-- 1 root root 21 Sep 27 05:28 s.txt
- -rwx------ 1 root root 5373 Sep 27 05:28 set.txt -rw-r--r-- 1 root root 21 Sep 27 05:28 s.txt
- /bin/echo -rw-r--r-- 1 root root 35 Sep 27 10:13 t.txt
- -rw-r--r-- 1 root root 35 S
-n num 控制每次输入的参数个数
假设你希望使用 rm 命令（该命令将作为 xargs 命令的参数）删除文件。然而，rm 只能接受有限数量的参数。如果你的参数列表超出该限制怎么办？xargs 的 -n 选项限制单个命令行的参数个数。
- [[email protected] ~/tmp/dir]#ls
- data.txt d.txt env2.txt env.txt export2.txt export.txt fuck.txt set.txt s.txt t.txt
- [[email protected] ~/tmp/dir]#ls |xargs -t -n 2 file
- file data.txt d.txt
- data.txt: ISO-8859 text
- d.txt: ISO-8859 text
- file env2.txt env.txt
- env2.txt: ASCII text, with very long lines
- env.txt: ASCII text, with very long lines
- file export2.txt export.txt
- export2.txt: ASCII text, with very long lines
- export.txt: ASCII text, with very long lines
- file fuck.txt set.txt
- fuck.txt: ASCII text
- set.txt: ASCII text, with very long lines
- file s.txt t.txt
- s.txt: ASCII text
- t.txt: ASCII text
- [[email protected] ~/tmp/dir]#
-E EOF 指定输入结束符
- [[email protected] ~/tmp/dir]#cat t.txt
- tata-hi -fuck - ok
- fuck _you _ you
- [[email protected] ~/tmp/dir]#xargs -a t.txt -E _
- tata-hi -fuck - ok fuck _you
- [[email protected] ~/tmp/dir]#xargs -a t.txt -E -
- tata-hi -fuck
-r xargs 默认是空参数comand也要执行一次，如使用-r参数遇到空参数则直接退出，不会再执行一次，避免程序执行错误。
- [[email protected] ~/tmp/dir]#ls
- data.txt d.txt env2.txt env.txt export2.txt export.txt fuck.txt set.txt s.txt t.txt
- [[email protected] ~/tmp/dir]#ls |grep Tata
- [[email protected] ~/tmp/dir]#ls |grep Tata |xargs -t
- /bin/echo
- [[email protected] ~/tmp/dir]#ls |grep Tata |xargs -t -r
- [[email protected] ~/tmp/dir]#
------------------------------------------------------------------------------------------------
MAN 手册
XARGS(1) XARGS(1)
NAME
xargs - build and execute command lines from standard input
SYNOPSIS
xargs [-0prtx] [-E eof-str] [-e[eof-str]] [--eof[=eof-str]] [--null]
[-d delimiter] [--delimiter delimiter] [-I replace-str] [-i[replace-
str]] [--replace[=replace-str]] [-l[max-lines]] [-L max-lines]
[--max-lines[=max-lines]] [-n max-args] [--max-args=max-args] [-s max-
chars] [--max-chars=max-chars] [-P max-procs] [--max-procs=max-procs]
[--interactive] [--verbose] [--exit] [--no-run-if-empty]
[--arg-file=file] [--show-limits] [--version] [--help] [command
[initial-arguments]]
DESCRIPTION
This manual page documents the GNU version of xargs. xargs reads items
from the standard input, delimited by blanks (which can be protected
with double or single quotes or a backslash) or newlines, and executes
the command (default is /bin/echo) one or more times with any initial-
arguments followed by items read from standard input. Blank lines on
the standard input are ignored.
Because Unix filenames can contain blanks and newlines, this default
behaviour is often problematic; filenames containing blanks and/or new-
lines are incorrectly processed by xargs. In these situations it is
better to use the -0 option, which prevents such problems. When using
this option you will need to ensure that the program which produces the
input for xargs also uses a null character as a separator. If that
program is GNU find for example, the -print0 option does this for you.
If any invocation of the command exits with a status of 255, xargs will
stop immediately without reading any further input. An error message
is issued on stderr when this happens.
OPTIONS
--arg-file=file
-a file
Read items from file instead of standard input. If you use this
option, stdin remains unchanged when commands are run.Other-
wise, stdin is redirected from /dev/null.
--null
-0 Input items are terminated by a null character insteadof by
whitespace, and the quotes and backslash are not special (every
character is taken literally). Disables the end of file string,
which is treated likeany other argument. Useful when input
items might contain white space, quote marks, or backslashes.
The GNUfind -print0 option produces input suitable for this
mode.
--delimiter=delim
-d delim
Input items are terminated by the specified character.Quotes
and backslash are not special; every character in the input is
taken literally.Disables the end-of-file string, which is
treated like any other argument. This can be used when the in-
put consists of simply newline-separated items, althoughit is
almost always better to design your program to use --null where
this is possible. The specified delimiter may be a single char-
acter, a C-style character escape such as \n, or an octal or
hexadecimal escape code.Octal and hexadecimal escape codes are
understood as for the printf command. Multibyte characters are
not supported.
-E eof-str
Set the end of file string to eof-str.If the end of file
string occurs as a line of input, the rest of the input is ig-
nored. If neither -E nor -e is used, no end of file string is
used.
--eof[=eof-str]
-e[eof-str]
This option is a synonym for the -E option. Use -E instead, be-
cause it is POSIX compliant while this option is not. If eof-
str is omitted, there is no end of file string. If neither -E
nor -e is used, no end of file string is used.
--help Print a summary of the options to xargs and exit.
-I replace-str
Replace occurrences of replace-str in the initial-arguments with
names read from standard input. Also, unquoted blanks do not
terminate input items; instead the separator is the newline
character. Implies -x and -L 1.
--replace[=replace-str]
-i[replace-str]
This option isa synonym for -Ireplace-str if replace-str is
specified, and for -I{} otherwise. This option is deprecated;
use -I instead.
-L max-lines
Use at most max-linesnonblank input lines per command line.
Trailing blanks cause an input line to be logically continued on
the next input line. Implies -x.
--max-lines[=max-lines]
-l[max-lines]
Synonym for the -L option. Unlike -L, the max-lines argument is
optional. If max-lines is not specified, it defaults to one.
The -l option is deprecated since the POSIX standard specifies
-L instead.
--max-args=max-args
-n max-args
Use at most max-args arguments per command line. Fewer than
max-argsarguments will be used if the size (see the -s option)
is exceeded, unless the -x option is given, in which case xargs
will exit.
--interactive
-p Prompt the user about whether to run each command line and read
a line from the terminal. Only run the command line if the re-
sponse starts with ‘y’ or ‘Y’. Implies -t.
--no-run-if-empty
-r If the standard input does not contain any nonblanks, do not run
the command. Normally, the command is run once even if there is
no input. This option is a GNU extension.
--max-chars=max-chars
-s max-chars
Use at most max-chars characters per command line, including the
command and initial-arguments and the terminating nulls at the
ends of the argument strings. The largest allowed value is sys-
tem-dependent, and is calculated as the argument length limit
for exec, less the size of your environment, less 2048 bytes of
headroom. If this value is more than 128KiB, 128Kib is used as
the default value; otherwise, the default value is the maximum.
1KiB is 1024 bytes.
--verbose
-t Print the command line on the standard error output before exe-
cuting it.
--version
Print the version number of xargs and exit.
--show-limits
Display the limits on the command-line length which are imposed
by the operating system, xargs’ choice of buffer size and the -s
option.
Pipe the input from /dev/null (and perhaps specify
--no-run-if-empty) if you don’t want xargs to do anything.
--exit
-x Exit if the size (see the -s option) is exceeded.
--max-procs=max-procs
-P max-procs
Run up to max-procs processes at a time; the default is 1. If
max-procs is 0, xargs will run as many processes as possible at
a time. Use the -n option with -P; otherwise chances are that
only one exec will be done.
EXAMPLES
find /tmp -name core -type f -print | xargs /bin/rm -f
Find files named core in or below the directory /tmp and delete them.
Note that this will work incorrectly if there are any filenames con-
taining newlines or spaces.
find /tmp -name core -type f -print0 | xargs -0 /bin/rm -f
Find files named core in or below the directory /tmp and delete them,
processing filenames in such a way that file ordirectory names con-
taining spaces or newlines are correctly handled.
find /tmp -depth -name core -type f -delete
Find files named core in or below the directory /tmp and delete them,
but more efficiently than in the previous example (because we avoid the
need to use fork(2) and exec(2) to launch rm and we don’t need the ex-
tra xargs process).
cut -d: -f1 < /etc/passwd | sort | xargs echo
Generates a compact listing of all the users on the system.
xargs sh -c ’emacs "$@" < /dev/tty’ emacs
Launches the minimum number of copies of Emacs needed, one after the
other, to edit the files listed on xargs’ standard input. This example
achieves the same effect as BSD’s -o option, but in a more flexible and
portable way.
EXIT STATUS
xargs exits with the following status:
0 if it succeeds
123 if any invocation of the command exited with status 1-125
124 if the command exited with status 255
125 if the command is killed by a signal
126 if the command cannot be run
127 if the command is not found
1 if some other error occurred.
Exit codes greater than 128 are used by the shell to indicate that a
program died due to a fatal signal.
STANDARDS CONFORMANCE
As of GNU xargs version 4.2.9, the default behaviour of xargs is not to
have a logical end-of-file marker. POSIX (IEEE Std 1003.1, 2004 Edi-
tion) allows this.
The -l and -i options appear in the 1997 version of the POSIX standard,
but do not appear in the 2004 version of the standard. Therefore you
should use -L and -I instead, respectively.
The POSIX standard allows implementations to have a limit on the size
of arguments to the exec functions. This limit could be as low as 4096
bytes including the size of the environment. For scriptsto be
portable, they must not rely on a larger value. However, I know of no
implementation whose actual limit is that small. The --show-limits op-
tion can be used to discover the actual limits in force on the current
system.
SEE ALSO
find(1), locate(1), locatedb(5), updatedb(1), fork(2), execvp(3), Find-
ing Files (on-line in Info, or printed)
BUGS
The -L optionis incompatible with the -I option, but perhaps should
not be.
It is not possible for xargs to be used securely, since there will al-
ways be a time gap between the production of the list of input files
and their use in the commands that xargs issues. If other users have
access to the system, they can manipulate the filesystem during this
time window to force the action of the commands xargs runs to apply to
files that you didn’t intend. For a more detailed discussion of this
and related problems, please refer to the ‘‘Security Considerations’’
chapter in the findutils Texinfo documentation.The -execdir option of
find can often be used as a more secure alternative.
When you use the -I option, each line read from the input is buffered
internally. This means that there is an upper limit on the length of
input line that xargs will accept when used with the -I option. To
work around this limitation, you can use the -s option to increase the
amount of buffer space that xargs uses, and you can also use an extra
invocation of xargs to ensure that very long lines do not occur. For
example:
somecommand | xargs -s 50000 echo | xargs -I ’{}’ -s 100000 rm ’{}’
Here, the first invocation of xargs has no input line length limit be-
cause it doesn’t use the -i option.The second invocation of xargs
does have such a limit, but we have ensured that the itnever encoun-
ters a line which is longer than it can handle. This is not an ideal
solution. Instead, the -i option should not impose a line length lim-
it, which is why this discussion appears in the BUGS section. The
problem doesn’t occur with the output of find(1) because it emits just
one filename per line.
The best way to report a bug is to use the form at http://savan-
nah.gnu.org/bugs/?group=findutils. The reason for this is that you
will then be able to track progress in fixing the problem. Other com-
ments about xargs(1) and about the findutils package in general can be
sent to the bug-findutils mailing list. To join the list, send email
to [email protected].
XARGS(1)