xargs
Linux Command – xargs ใช้ในการสร้างคำสั่งใหม่จาก ouput ที่ได้ก่อนหน้า
คำสั่ง
<command – output> | xargs <command>
ลบ file ชื่อ core ภายใต้ directory /tmp ทั้งหมด
$ find /tmp -name core -type f -print | xargs /bin/rm -f
or
$ find /tmp -name core -type f -print0 | xargs -0 /bin/rm -f
โครงสร้างคำสั่ง
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]
[--process-slot-var=name] [--interactive] [--verbose] [--exit] [--no-run-if-empty] [--arg-file=file] [--show-limits] [--version] [--help] [command [initial-arguments]]
รายละเอียด
เป็นคำสั่งที่ใช้ในการสร้างคำสั่งใหม่จาก ouput ที่ได้ก่อนหน้า ใช้งานโดยวางไว้หลัง pipeline (|) เพื่อนำเอา ouput ก่อนนหน้ามาใช้งานเป็นตัวแปลสำหรับ command ที่ xargs จะใช้รันคำสั่ง
Option
-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 pro‐ duces 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. Otherwise, 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 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. 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 ignored. 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, because 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 implementation-defined limit (which is shown with --show-limits). You cannot decrease it below 1. xargs never terminates its commands; 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 ouptut 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 separate resources). -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 response starts with `y' or `Y'. Implies -t. --process-slot-var=name Set the environment variable name to a unique value in each running child process. Values are reused once child processes exit. This can be used in a rudimentary load dis‐ tribution 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 system-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 constraints. --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 executing 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.
กลุ่มคำสั่ง
find(1), locate(1), locatedb(5), updatedb(1), fork(2), execvp(3), kill(1), signal(7),
Reference:
Author: Suphakit Annoppornchai
Credit: https://saixiii.com
