# Bash 的 truncate 命令

truncate OPTION... FILE...

$ truncate -s 10k 1.txt             # 将 1.txt 的大小设为 10k，文件不存在时自动创建
$ ls -l 1.txt
-rw-rw-r-- 1 planc planc 10240 Dec  6 12:27 1.txt
$ truncate -s 1 -o 1.txt            # 将 1.txt 的大小设为一个 I/O 块
$ ls -l 1.txt
-rw-rw-r-- 1 planc planc 4096 Dec  6 12:28 1.txt

$ truncate -s 1k 2.txt              # 创建一个 1k 大小的文件
$ truncate -r 2.txt 1.txt           # 将 1.txt 的大小设为和 2.txt 一样
$ ls -l 1.txt
-rw-rw-r-- 1 planc planc 1024 Dec  6 12:30 1.txt
$ truncate -r 2.txt -s +1k 1.txt    # 将 1.txt 的大小设为比 2.txt 大 1k
$ ls -l 1.txt
-rw-rw-r-- 1 planc planc 2048 Dec  6 12:32 1.txt

TRUNCATE(1)                      User Commands                     TRUNCATE(1)

NAME
       truncate - shrink or extend the size of a file to the specified size

SYNOPSIS
       truncate OPTION... FILE...

DESCRIPTION
       Shrink or extend the size of each FILE to the specified size

       A FILE argument that does not exist is created.

       If  a  FILE  is larger than the specified size, the extra data is lost.
       If a FILE is shorter, it is  extended  and  the  sparse  extended  part
       (hole) reads as zero bytes.

       Mandatory  arguments  to  long  options are mandatory for short options
       too.

       -c, --no-create
              do not create any files

       -o, --io-blocks
              treat SIZE as number of IO blocks instead of bytes

       -r, --reference=RFILE
              base size on RFILE

       -s, --size=SIZE
              set or adjust the file size by SIZE bytes

       --help display this help and exit

       --version
              output version information and exit

       The SIZE argument is an integer and  optional  unit  (example:  10K  is
       10*1024).   Units are K,M,G,T,P,E,Z,Y,R,Q (powers of 1024) or KB,MB,...
       (powers of 1000).  Binary prefixes can be used, too: KiB=K, MiB=M,  and
       so on.

       SIZE may also be prefixed by one of the following modifying characters:
       '+' extend by, '-' reduce by, '<' at most, '>' at least, '/' round down
       to multiple of, '%' round up to multiple of.

AUTHOR
       Written by Padraig Brady.

REPORTING BUGS
       GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
       Report any translation bugs to <https://translationproject.org/team/>

COPYRIGHT
       Copyright  ©  2023  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
       dd(1), truncate(2), ftruncate(2)

       Full documentation <https://www.gnu.org/software/coreutils/truncate>
       or available locally via: info '(coreutils) truncate invocation'

GNU coreutils 9.4                 April 2024                       TRUNCATE(1)