Linux system admin command(basic)

Linux Command
1. output files
cat -- concatenate files and print on the standard output
tac -- concatenate and print file in reverse
nl -- number lines of file
head -- output the first part of file
tail -- output the last part of file

2. summarizing files
wc -- print newline, word, and byte counts for each file
     eg. $wc -l -c test      30(line) 557(byte) test

3. sort files
sort -- sort lines of text files

eg. sort缺省默认空格和tab键为分隔符。其他方式分隔，使用-t选项。缺省以第1列来排序，即-k1 -n 指定分类是域上的数字分类。 如编辑文件1111.txt sdsad 311 315 asd3f wdasd 551 133 adsff sdsad 606 44 fgfdgdf wdwew 77 599 gghgf eeese 23 22 fgdf eeese 23 22 fgdf dfdff 78 55 fdgd    -k 使用k做分类排序,如按第2列来分类排序 $ sort -k2 1111.txt eeese 23 22 fgdf eeese 23 22 fgdf sdsad 311 315 asd3f wdasd 551 133 adsff sdsad 606 44 fgfdgdf wdwew 77 599 gghgf dfdff 78 55 fdgd     -n 指定分类列上按数值来分类排序，如第按第2列数值大小来分类 $ sort -k2n 1111.txt eeese 23 22 fgdf eeese 23 22 fgdf wdwew 77 599 gghgf dfdff 78 55 fdgd sdsad 311 315 asd3f wdasd 551 133 adsff sdsad 606 44 fgfdgdf     -u 去除重复的行，即完全一样的行，只保留一行 $ sort -k2n -u 1111.txt eeese 23 22 fgdf 只有1行了 wdwew 77 599 gghgf dfdff 78 55 fdgd sdsad 311 315 asd3f wdasd 551 133 adsff sdsad 606 44 fgfdgdf

4. unique filesuniq --  report or omit repeated lines
        -d:  only print duplicate lines
       -u:  only print unique lines
5. compare filesdiff -- compare files line by line
     -y: output in two colums
      -c: output lines of copied context (上下文输出格式)
      -u: output lines of unified context

eg. a.txt     abc     hello b.txt     cba     hello $ diff -y a.txt b.txt -W 50 abc              |    cba hello            hello $ diff -c a.txt b.txt *** a.txt    2010-12-13 22:15:13.000000000 +0800 --- b.txt    2010-12-13 22:15:21.000000000 +0800 *************** *** 1,2 **** ! abc   hello --- 1,2 ---- ! cba   hello $ diff -u a.txt b.txt --- a.txt    2010-12-13 22:15:13.000000000 +0800 +++ b.txt    2010-12-13 22:15:21.000000000 +0800 @@ -1,2 +1,2 @@ -abc +cba  test

6. operating on characters
tr -- translate or delete characters
      -c: 取SET1的反义，所有不在SET1中的字符
      -d: delete characters in SET1
      -s: 浓缩重复的字符。如果标准输入中连续重复出现SET1里所列的字符，则将其浓缩成一个。或者将其浓缩成SET1中的字符
ps:

$echo "chennnrui123" | tr -d "cr123" hennnui $echo "chennnrui123" | tr -s "[a-z]" chenrui123 $echo "abc123def" | tr -cs "[a-z]" " " abc def $echo "abc123def" | tr -cs "[a-z]" " " abc def

Others
alias -- redefine command
eg.   alias ls='ls -lh'