Linux中的less命令及示例

Less命令是一个Linux实用程序，可用于一次读取一页（一个屏幕）文本文件的内容。它的访问速度更快，因为如果文件很大，它不会访问完整的文件，而是逐页访问。

例如，如果它是一个大文件，并且您正在使用任何文本编辑器读取它，那么完整的文件将加载到主内存中。less命令不会加载整个文件，而是一部分一部分地加载，这会加快加载速度。

语法：

less filename

注： 我在用 启动信息 在以下示例中，输出为less命令的输入。

例如：如果你想阅读 dmesg命令 ，最好用较少的命令来使用它

dmesg | less

输出：

[    0.000000] microcode: microcode updated early to revision 0x21, date = 2017-11-20[    0.000000] random: get_random_bytes called from start_kernel+0x42/0x504 with crng_init=0[    0.000000] Linux version 4.13.0-26-generic (buildd@lgw01-amd64-031) (gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.5)) #29~16.04.2-Ubuntu SMP Tue Jan 9 22:00:44 UTC 2018 (Ubuntu 4.13.0-26.29~16.04.2-generic 4.13.13)[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.13.0-26-generic.efi.signed root=UUID=993a37f2-7ea9-43a3-b652-5b26bb879797 ro quiet splash vt.handoff=7[    0.000000] KERNEL supported cpus:[    0.000000]   Intel GenuineIntel[    0.000000]   AMD AuthenticAMD[    0.000000]   Centaur CentaurHauls[    0.000000] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers'[    0.000000] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers'[    0.000000] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers'[    0.000000] x86/fpu: xstate_offset[2]:  576, xstate_sizes[2]:  256[    0.000000] x86/fpu: Enabled xstate features 0x7, context size is 832 bytes, using 'standard' format.[    0.000000] e820: BIOS-provided physical RAM map:[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000006efff] usable[    0.000000] BIOS-e820: [mem 0x000000000006f000-0x000000000006ffff] reserved[    0.000000] BIOS-e820: [mem 0x0000000000070000-0x0000000000087fff] usable[    0.000000] BIOS-e820: [mem 0x0000000000088000-0x00000000000bffff] reserved[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000094d5ffff] usable[    0.000000] BIOS-e820: [mem 0x0000000094d60000-0x0000000095d5ffff] reserved[    0.000000] BIOS-e820: [mem 0x0000000095d60000-0x000000009a36efff] usable[    0.000000] BIOS-e820: [mem 0x000000009a36f000-0x000000009aebefff] reserved[    0.000000] BIOS-e820: [mem 0x000000009aebf000-0x000000009afbefff] ACPI NVS[    0.000000] BIOS-e820: [mem 0x000000009afbf000-0x000000009affefff] ACPI data[    0.000000] BIOS-e820: [mem 0x000000009afff000-0x000000009affffff] usable[    0.000000] BIOS-e820: [mem 0x000000009b000000-0x000000009f9fffff] reserved[    0.000000] BIOS-e820: [mem 0x00000000e0000000-0x00000000efffffff] reserved[    0.000000] BIOS-e820: [mem 0x00000000fe101000-0x00000000fe112fff] reserved[    0.000000] BIOS-e820: [mem 0x00000000feb00000-0x00000000feb0ffff] reserved[    0.000000] BIOS-e820: [mem 0x00000000fec00000-0x00000000fec00fff] reserved[    0.000000] BIOS-e820: [mem 0x00000000fed00000-0x00000000fee00fff] reserved[    0.000000] BIOS-e820: [mem 0x00000000ffc00000-0x00000000ffffffff] reserved[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000025f5fffff] usable[    0.000000] NX (Execute Disable) protection: active[    0.000000] e820: update [mem 0x93c97018-0x93ca7057] usable ==> usable[    0.000000] e820: update [mem 0x93c97018-0x93ca7057] usable ==> usable[    0.000000] e820: update [mem 0x93c8a018-0x93c96057] usable ==> usable[    0.000000] e820: update [mem 0x93c8a018-0x93c96057] usable ==> usable:

最常用的选项：

-E:使less在第一次到达文件末尾时自动退出。 -f：强制打开非常规文件。 -F：如果整个文件可以在第一个屏幕上显示，则会导致较少的退出 -g：突出显示上次搜索命令找到的字符串 -G：抑制搜索命令找到的字符串的所有高亮显示 -i:导致搜索忽略案例 -n：抑制行号 -p pattern：它告诉less从文件中第一个出现的模式开始 -s：将连续的空行压缩为一个空行

命令使用和选项：

dmesg | less -p "failure"

上面的命令告诉less在文件中第一次出现模式“failure”时启动。

输出：

[  368.748104] wlp2s0: failed to remove key (1, ff:ff:ff:ff:ff:ff) from hardware (-22)[  372.254014] wlp2s0: authenticate with a0:55:4f:27:bd:01[  372.257112] wlp2s0: send auth to a0:55:4f:27:bd:01 (try 1/3)[  372.261055] wlp2s0: authenticated[  372.264307] wlp2s0: associate with a0:55:4f:27:bd:01 (try 1/3)[  372.270621] wlp2s0: RX AssocResp from a0:55:4f:27:bd:01 (capab=0x431 status=0 aid=199)[  372.272312] wlp2s0: associated[  372.357068] wlp2s0: Limiting TX power to 30 (30 - 0) dBm as advertised by a0:55:4f:27:bd:01[  682.255302] wlp2s0: disassociated from a0:55:4f:27:bd:01 (Reason: 1=UNSPECIFIED)[  682.304134] wlp2s0: failed to remove key (1, ff:ff:ff:ff:ff:ff) from hardware (-22)[  685.809837] wlp2s0: authenticate with a0:55:4f:27:bd:01

dmesg | less -N

它将显示输出以及行号 输出：

1 [    0.000000] microcode: microcode updated early to revision 0x21, date = 2017-11-20      2 [    0.000000] random: get_random_bytes called from start_kernel+0x42/0x504 with crng_init=0      3 [    0.000000] Linux version 4.13.0-26-generic (buildd@lgw01-amd64-031) (gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.5)) #2      3 9~16.04.2-Ubuntu SMP Tue Jan 9 22:00:44 UTC 2018 (Ubuntu 4.13.0-26.29~16.04.2-generic 4.13.13)      4 [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.13.0-26-generic.efi.signed root=UUID=993a37f2-7ea9-43a3-b652-5b26bb879797 ro qu      4 iet splash vt.handoff=7      5 [    0.000000] KERNEL supported cpus:      6 [    0.000000]   Intel GenuineIntel      7 [    0.000000]   AMD AuthenticAMD      8 [    0.000000]   Centaur CentaurHauls      9 [    0.000000] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers'     10 [    0.000000] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers'     11 [    0.000000] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers'     12 [    0.000000] x86/fpu: xstate_offset[2]:  576, xstate_sizes[2]:  256

less -F filenameeg. less -F /home/mandeep/test/first.erl

它不会给出任何输出，因为文件可以在单个屏幕上显示。

less /home/mandeep/test/first.erl

这些是上述测试文件的内容，可以在单个屏幕上显示。

-module(first).-export([fib/1]).fib(X) when X     1;fib(X) when X >= 2 ->    fib(X - 1) + fib(X - 2).

– 曼迪星

参考资料： 1) 维基百科 2） linux手册页