Linux系统命令总结--查看文件内容

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Linux系统命令总结–查看文件内容

查看文件类型

  1. file命令

    file命令file --help

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    Usage: file [OPTION...] [FILE...]
    Determine type of FILEs.

          --help                 display this help and exit
      -v, --version              output version information and exit
      -m, --magic-file LIST      use LIST as a colon-separated list of magic
                                   number files
      -z, --uncompress           try to look inside compressed files
      -Z, --uncompress-noreport  only print the contents of compressed files
      -b, --brief                do not prepend filenames to output lines
      -c, --checking-printout    print the parsed form of the magic file, use in
                                   conjunction with -m to debug a new magic file
                                   before installing it
      -e, --exclude TEST         exclude TEST from the list of test to be
                                   performed for file. Valid tests are:
                                   apptype, ascii, cdf, compress, elf, encoding,
                                   soft, tar, text, tokens
      -f, --files-from FILE      read the filenames to be examined from FILE
      -F, --separator STRING     use string as separator instead of `:'
      -i, --mime                 output MIME type strings (--mime-type and
                                   --mime-encoding)
          --apple                output the Apple CREATOR/TYPE
          --extension            output a slash-separated list of extensions
          --mime-type            output the MIME type
          --mime-encoding        output the MIME encoding
      -k, --keep-going           don't stop at the first match
      -l, --list                 list magic strength
      -L, --dereference          follow symlinks (default if POSIXLY_CORRECT is set)
      -h, --no-dereference       don't follow symlinks (default if POSIXLY_CORRECT is not set) (default)
      -n, --no-buffer            do not buffer output
      -N, --no-pad               do not pad output
      -0, --print0               terminate filenames with ASCII NUL
      -p, --preserve-date        preserve access times on files
      -P, --parameter            set file engine parameter limits
                                   indir        15 recursion limit for indirection
                                   name         30 use limit for name/use magic
                                   elf_notes   256 max ELF notes processed
                                   elf_phnum   128 max ELF prog sections processed
                                   elf_shnum 32768 max ELF sections processed
      -r, --raw                  don't translate unprintable chars to \ooo
      -s, --special-files        treat special (block/char devices) files as
                                 ordinary ones
      -C, --compile              compile file specified by -m
      -d, --debug                print debugging messages

    file命令主要用来查看文件的类型。

    | 参数 | 作用 |
    | —- | ———————————————————— |
    | -b | 结果不输出文件名 |
    | -z | 尝试解压压缩文件 |
    | -f | 指定名称文件，其中内容有一个或者多个文件名称时，依序辨识这些文件 |
    | -L | 直接显示符号链接指向的文件 |
    | -v | 显示版本信息 |
    | | |
    | | |

查看文件内容

  1. cat命令

    cat --help 显示cat命令帮助

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Usage: cat [OPTION]... [FILE]...
Concatenate FILE(s) to standard output.

With no FILE, or when FILE is -, read standard input.

  -A, --show-all           equivalent to -vET
  -b, --number-nonblank    number nonempty output lines, overrides -n
  -e                       equivalent to -vE
  -E, --show-ends          display $ at end of each line
  -n, --number             number all output lines
  -s, --squeeze-blank      suppress repeated empty output lines
  -t                       equivalent to -vT
  -T, --show-tabs          display TAB characters as ^I
  -u                       (ignored)
  -v, --show-nonprinting   use ^ and M- notation, except for LFD and TAB
      --help     display this help and exit
      --version  output version information and exit

cat相关命令

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#查看文件
$ cat test.sh
echo date;

#-n参数给所有行加上行号
$ cat -n test.sh
     1  echo date;

#只给有文本的行加上行号，可以用-b参数
$ cat -b test.sh
     1  echo date;

     2  echo time;
     
#如果不想出现制表符，可以用-T参数，-T参数会用^I字符组合去替换文中的所有制表符
$ cat -T test.sh
echo date;

echo time;

#使用-s参数来去除多余的空行，原来文件之间有多个空行
$ cat -s test.sh
echo date;

echo time;

#使用-e参数来使得每一行的末尾都以$结尾
$ cat -e test.sh
echo date;$
$
$
$
$
$
$
$
echo time;$
  1. more命令

    cat的缺陷在于一旦运行就无法控制后面操作，为了解决这个问题，开发人员编写了more命令。more命令会显示文本文件的内容，但是会在显示每页数据之后停下来。

    more --help

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    Usage:
     more [options] <file>...

    A file perusal filter for CRT viewing.

    Options:
     -d          display help instead of ringing bell
     -f          count logical rather than screen lines
     -l          suppress pause after form feed
     -c          do not scroll, display text and clean line ends
     -p          do not scroll, clean screen and display text
     -s          squeeze multiple blank lines into one
     -u          suppress underlining
     -<number>   the number of lines per screenful
     +<number>   display file beginning from line number
     +/<string>  display file beginning from search string match

    more命令的相关参数

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    # more命令的相关参数,显示相关帮助信息
    more -d test.sh
    ...
    222
    222
    --More--(16%)[Press space to continue, 'q' to quit.]

    # more命令-f参数
    ...
  2. less命令

    less 命令实际上是more命令的升级版（名称由俗语less is more得来），

查看部分文件

  1. tail命令

    tail命令tail --help

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    Usage: tail [OPTION]... [FILE]...
    Print the last 10 lines of each FILE to standard output.
    With more than one FILE, precede each with a header giving the file name.

    With no FILE, or when FILE is -, read standard input.

    Mandatory arguments to long options are mandatory for short options too.
      -c, --bytes=[+]NUM       output the last NUM bytes; or use -c +NUM to
                                 output starting with byte NUM of each file
      -f, --follow[={name|descriptor}]
                               output appended data as the file grows;
                                 an absent option argument means 'descriptor'
      -F                       same as --follow=name --retry
      -n, --lines=[+]NUM       output the last NUM lines, instead of the last 10;
                                 or use -n +NUM to output starting with line NUM
          --max-unchanged-stats=N
                               with --follow=name, reopen a FILE which has not
                                 changed size after N (default 5) iterations
                                 to see if it has been unlinked or renamed
                                 (this is the usual case of rotated log files);
                                 with inotify, this option is rarely useful
          --pid=PID            with -f, terminate after process ID, PID dies
      -q, --quiet, --silent    never output headers giving file names
          --retry              keep trying to open a file if it is inaccessible
      -s, --sleep-interval=N   with -f, sleep for approximately N seconds
                                 (default 1.0) between iterations;
                                 with inotify and --pid=P, check process P at
                                 least once every N seconds
      -v, --verbose            always output headers giving file names
      -z, --zero-terminated    line delimiter is NUL, not newline
          --help     display this help and exit
          --version  output version information and exit

    tail命令：显示文件最后几行的内容。默认显示文件末尾10行。

    比如我们创建了一个包含20行文本的文本文件。使用cat命令显示该文件的全部内容如下：

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    $ cat log_file
    line1
    line2
    line3
    line4
    line5
    Hello World - line 6
    line7
    line8
    line9
    line10
    line11
    Hello again - line 12
    line13
    line14
    line15
    Sweet - line16
    line17
    line18
    line19
    Last line - line20
    $

    现在显示的是整个文件，使用tail命令浏览文件最后10行的效果：

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    $ tail log_file
    line11
    Hello again - line 12
    line13
    line14
    line15
    Sweet - line16
    line17
    line18
    line19
    Last line - line20
    $

    可以向tail命令加入-n参数来修改所显示的行数。下面的例子中，通过加入-n 2使tail命令只显示文件的最后两行。

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    $ tail -n 2 log_file
    line19
    Last line - line20
    $

    还可以在通过tail命令 加号显示某行之后的行数

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    $ tail -n +10 log_file
    line10
    line11
    Hello again - line 12
    line13
    line14
    line15
    Sweet - line16
    line17
    line18
    line19
    Last line - line20

    -f参数是tail命令的一个突出特性，允许你在其他进程中使用该文件时查看文件的内容。tail会保持活动状态，并且不断的显示添加文件中的内容。

  2. head命令

    首先通过head --help来查看head命令的使用方法

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    Usage: head [OPTION]... [FILE]...
    Print the first 10 lines of each FILE to standard output.
    With more than one FILE, precede each with a header giving the file name.

    With no FILE, or when FILE is -, read standard input.

    Mandatory arguments to long options are mandatory for short options too.
      -c, --bytes=[-]NUM       print the first NUM bytes of each file;
                                 with the leading '-', print all but the last
                                 NUM bytes of each file
      -n, --lines=[-]NUM       print the first NUM lines instead of the first 10;
                                 with the leading '-', print all but the last
                                 NUM lines of each file
      -q, --quiet, --silent    never print headers giving file names
      -v, --verbose            always print headers giving file names
      -z, --zero-terminated    line delimiter is NUL, not newline
          --help     display this help and exit
          --version  output version information and exit

    head命令查看文件的前10行

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    $ head log_file
    line1
    line2
    line3
    line4
    line5
    Hello World - line 6
    line7
    line8
    line9
    line10
    $

    也可以使用参数-n 来指定显示的行数,比如head -n 5 log_file显示log_file的前5行

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    $ head -n 5 log_file
    line1
    line2
    line3
    line4
    line5

    也可以通过添加减号，指定不显示最后几行，比如head -n -5 log_file

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    $ head -n -5 log_file
    line1
    line2
    line3
    line4
    line5
    Hello World - line 6
    line7
    line8
    line9
    line10
    line11
    Hello again - line 12
    line13
    line14
    line15

    一般文件头不会发生变化，所以没有-f参数

  3. head和tail命令的组合使用

    比如你想显示某个文件的第10行，我们可以组合使用head和tail命令

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    $ tail -n +10 log_file |head -n 1
    line10

    再比如从第11行显示，但是不包括最后三行

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    $ head -n -3 log_file | tail -n +11
    line11
    Hello again - line 12
    line13
    line14
    line15
    Sweet - line16
    line17

    再比如显示前20行，但是从第11行开始

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    $ head -n 20 log_file | tail -n +11
    line11
    Hello again - line 12
    line13
    line14
    line15
    Sweet - line16
    line17
    line18
    line19
    Last line - line20

    可以看出，组合head和tail命令可以产生更加强大的功能。

参考文献

《Linux命令行和shell脚本编程大全》