#Bash 的 xargs 命令
xargs [OPTION]... [CMD [ARG]...]
功能
从标准输入构建命令行并执行。
xargs从标准输入读取以空格（可用双引号、单引号或反斜杠保护）或换行符分隔的项，并执行命令（默认为 echo）一次或多次，每次执行的参数可以是任意值，后跟从标准输入读取的项。标准输入中的空行将被忽略。
类型
可执行文件（/usr/bin/xargs），属于 findutils。
参数
OPTIONS选项：-0,--null- 输入项以空字符（\0）作为分隔符（而非默认的空格或换行符），引号和反斜杠不再特殊处理-a file,--arg-file=file- 从文件而非标准输入读取数据--delimiter=delim,-d delim- 输入项以delim作为分隔符-E eof-str- 以eof-str作为文件结束符-e[eof-str],--eof[=eof-str]- 同-E；不建议使用此选项-I replace-str- 将ARG中出现的replace-str替换为从标准输入读取的字符串；使用此选项每行 1 行执行一次命令-i[replace-str],--replace[=replace-str]-同；已弃用-I-L max-lines- 每max-lines行输入执行一行命令-l[max-lines],--max-lines[=max-lines]-同；已弃用-L-n max-args,--max-args=max-args- 每条命令行最多可以使用 max-args 个参数-P max-procs,--max-procs=max-procs- 一次可最多运行max-procs个进程；默认为 1-o,--open-tty- 在执行命令之前，先在子进程中将 stdin 重新打开为/dev/tty-p,--interactive- 交互式执行；运行每条命令前先进行询问--process-slot-var=name- 在每个运行的子进程中，将环境变量name设置为进程的唯一编号-r,--no-run-if-empty- 如果标准输入不包含任何非空白字符，则不执行该命令-s max-chars,--max-chars=max-chars- 每条命令行最多使用max-chars个字符，包括命令、初始参数以及参数字符串末尾的终止空字符--show-limits- 显示资源限制-t,--verbose- 打印详细信息-x,--exit- 如果超出-s选项的大小限制，则退出--help- 显示帮助--version- 显示版本
CMD- 命令；省略时默认为echoARG- 初始参数列表；从标准输入中读取的参数会追加在此之后
#示例
基础使用
$ echo hello | xargs # 等价于 echo hello | xargs echo
hello
按行分割命令
$ echo -e "hello\nworld" | xargs # 默认执行一次命令
hello world
$ echo -e "hello\nworld" | xargs -L 1 # 每 1 行执行一次命令
hello
world
按参数数量分割命令
$ echo 1 2 3 4 5 | xargs # 默认执行一次命令
1 2 3 4 5
$ echo 1 2 3 4 5 | xargs -n 2 # 每两个参数执行一次命令
1 2
3 4
5
占位符替换
$ echo -e "eye\ntooth" | xargs -I {} echo 'A(n) {} for a(n) {}' # 将 {} 替换为读取的参数，并且每一行执行一次命令
A(n) eye for a(n) eye
A(n) tooth for a(n) tooth
$ ls
1.txt 2.txt 3.txt
$ ls *.txt | xargs -I {} basename {} .txt | xargs -I {} mv {}.txt {}.md # 将 .txt 文件批量重命名为 .md 文件
$ ls
1.md 2.md 3.md
#推荐阅读
#手册
XARGS(1) General Commands Manual XARGS(1)
NAME
xargs - build and execute command lines from standard input
SYNOPSIS
xargs [options] [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 echo) one or more times with any initial-argu‐
ments followed by items read from standard input. Blank lines on the
standard input are ignored.
The command line for command is built up until it reaches a system-de‐
fined limit (unless the -n and -L options are used). The specified
command will be invoked as many times as necessary to use up the list
of input items. In general, there will be many fewer invocations of
command than there were items in the input. This will normally have
significant performance benefits. Some commands can usefully be exe‐
cuted in parallel too; see the -P option.
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
-0, --null
Input items are terminated by a null character instead of by
whitespace, and the quotes and backslash are not special (every
character is taken literally). Disables the end of file string,
which is treated like any other argument. Useful when input
items might contain white space, quote marks, or backslashes.
The GNU find -print0 option produces input suitable for this
mode.
-a file, --arg-file=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.
--delimiter=delim, -d delim
Input items are terminated by the specified character. The
specified delimiter may be a single character, a C-style charac‐
ter 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. When
processing the input, quotes and backslash are not special;
every character in the input is taken literally. The -d option
disables any end-of-file string, which is treated like any other
argument. You can use this option when the input consists of
simply newline-separated items, although it is almost always
better to design your program to use --null where this is possi‐
ble.
-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.
-e[eof-str], --eof[=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.
-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.
-i[replace-str], --replace[=replace-str]
This option is a synonym for -Ireplace-str if replace-str is
specified. If the replace-str argument is missing, the effect
is the same as -I{}. This option is deprecated; use -I instead.
-L max-lines
Use at most max-lines nonblank input lines per command line.
Trailing blanks cause an input line to be logically continued on
the next input line. Implies -x.
-l[max-lines], --max-lines[=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.
-n max-args, --max-args=max-args
Use at most max-args arguments per command line. Fewer than
max-args arguments will be used if the size (see the -s option)
is exceeded, unless the -x option is given, in which case xargs
will exit.
-P max-procs, --max-procs=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 or the -L option with -P; otherwise
chances are that only one exec will be done. While xargs is
running, you can send its process a SIGUSR1 signal to increase
the number of commands to run simultaneously, or a SIGUSR2 to
decrease the number. You cannot increase it above an implemen‐
tation-defined limit (which is shown with --show-limits). You
cannot decrease it below 1. xargs never terminates its com‐
mands; when asked to decrease, it merely waits for more than one
existing command to terminate before starting another.
Please note that it is up to the called processes to properly
manage parallel access to shared resources. For example, if
more than one of them tries to print to stdout, the output will
be produced in an indeterminate order (and very likely mixed up)
unless the processes collaborate in some way to prevent this.
Using some kind of locking scheme is one way to prevent such
problems. In general, using a locking scheme will help ensure
correct output but reduce performance. If you don't want to
tolerate the performance difference, simply arrange for each
process to produce a separate output file (or otherwise use sep‐
arate resources).
-o, --open-tty
Reopen stdin as /dev/tty in the child process before executing
the command. This is useful if you want xargs to run an inter‐
active application.
-p, --interactive
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.
--process-slot-var=name
Set the environment variable name to a unique value in each run‐
ning child process. Values are reused once child processes ex‐
it. This can be used in a rudimentary load distribution scheme,
for example.
-r, --no-run-if-empty
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.
-s max-chars, --max-chars=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. xargs automatically adapts to tighter con‐
straints.
--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.
-t, --verbose
Print the command line on the standard error output before exe‐
cuting it.
-x, --exit
Exit if the size (see the -s option) is exceeded.
--help Print a summary of the options to xargs and exit.
--version
Print the version number of xargs and exit.
The options --max-lines (-L, -l), --replace (-I, -i) and --max-args
(-n) are mutually exclusive. If some of them are specified at the same
time, then xargs will generally use the option specified last on the
command line, i.e., it will reset the value of the offending option
(given before) to its default value. Additionally, xargs will issue a
warning diagnostic on stderr. The exception to this rule is that the
special max-args value 1 ('-n1') is ignored after the --replace option
and its aliases -I and -i, because it would not actually conflict.
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 or directory 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.
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 -o option is an extension to the POSIX standard for better compati‐
bility with BSD.
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 scripts to 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.
BUGS
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 it never encounters a
line which is longer than it can handle. This is not an ideal solu‐
tion. Instead, the -i option should not impose a line length limit,
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.
REPORTING BUGS
GNU findutils online help: <https://www.gnu.org/software/findu‐
tils/#get-help>
Report any translation bugs to <https://translationproject.org/team/>
Report any other issue via the form at the GNU Savannah bug tracker:
<https://savannah.gnu.org/bugs/?group=findutils>
General topics about the GNU findutils package are discussed at the
bug-findutils mailing list:
<https://lists.gnu.org/mailman/listinfo/bug-findutils>
COPYRIGHT
Copyright © 1990-2022 Free Software Foundation, Inc. License GPLv3+:
GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
SEE ALSO
find(1), kill(1), locate(1), updatedb(1), fork(2), execvp(3), locat‐
edb(5), signal(7)
Full documentation <https://www.gnu.org/software/findutils/xargs>
or available locally via: info xargs
XARGS(1)