最後更新: 2022-08-01

介紹

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)

目錄

常用參數

-r, --no-run-if-empty             # 當 stdin 沒有 input 就不行 command
                                              (Normally, the command is run once even if there is no input.)

-a file, --arg-file=file             # Read arguments from FILE (instead of standard input)

-p, --interactive                    # Prompt the user about whether to run each command line

-d delim, --delimiter=delim   # Multibyte characters are not supported
                                          # a C-style character escape such as \n, or an octal or hexadecimal escape code

-0, --null                             # Input items are terminated by a null character instead of by whitespace

max-X

-L max-lines                # Use at most max-lines nonblank input lines per command line (Implies -x)

-n max-args                # Use at most max-args arguments per command line

-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
                                  # The largest allowed value is system-dependent,
                                  # and is calculated as the argument length limit for exec

-x, --exit                             # Exit if the size (see the -s option) is exceeded.

-s max-chars                       # Use at most max-chars characters per command line
                                          # including the terminating nulls at the ends of the argument strings.
                                          # The largest allowed value is  system-dependent
                                          # (The argument length limit for exec)
                                         # If this value is more  than 128KiB, 128KiB is used as the default value;

Checking: The argument length limit for exec

getconf ARG_MAX

2097152            # 相當於 2KiB

-E eof-str                            # Set the end of file string to eof-str.

-I replace-str                       # 以 placeholder 取化 args

Example

files.txt 的內容

1 a
2 b
3 c
4 d

Example 1: Basic Usage

cat files.txt | xargs echo

cat files.txt | xargs           # 結果與上一句相同, 預設 CMD 係 echo

# 預設是一行過全輸出, 亦即是

1 a 2 b 3 c 4 d

more

"ls -1 /etc/ssh/*key.pub | xargs" 與 "ls /etc/ssh/*key.pub | xargs" 相同 result

Example 2: read args from file

xargs -a files.txt echo

xargs -a files.txt

Example 3: # 問是否執行

xargs -p -a files.txt rm

rm 1 a 2 b 3 c 4 d ?...

Example 4: 每 N 一組組執行

# 每 1 行 一組, 相當於 `cat`

xargs -a files.txt -L 1 echo

# 每 2 行 一組

xargs -a files.txt -L 2

1 a 2 b
3 c 4 d

# 每  3 個 一組

xargs -a files.txt -n 3

1 a 2
b 3 c
4 d

Notes

ls -1 /etc/ssh/*key.pub | xargs -L 1 ssh-keygen -l -f

ls /etc/ssh/*key.pub | xargs -n 1 ssh-keygen -l -f

Example 5: 安裝一堆 PHP Package

yum list | grep php56u | grep -v -e debuginfo -e devel | cut -f 1 -d' ' > php-package.txt

xargs -a php-package.txt yum install

進階應該

-I replace-str

# Replace occurrences of replace-str in the initial-arguments with names read from stdin
# replace-str 可以理解為一個 placeholder
# Implies -x and -L 1

應用 1: Delete File

# 為了安全, 必須加上 tmp/

xargs -a list.txt -I{} mv {} tmp/

應用 2: 轉 Folder 名

xargs -a FolderName.txt -I{} doveadm mailbox mutf7 -7 "{}"