Awk command exercise

    As one of the three swordsmen of the text ,awk The command has powerful functions in filtering data . Use awk On command , Fields separated by separators （ Column column, Domain field） Mark $1,$2...$n It's called a domain identifier ,$0 For all domains （ and shell Medium variable $ They have different meanings ）, Each line becomes record, If omitted action, By default print $0 The operation of .

    The requirements of this exercise are ： Use awk Get... Separated by colons /ettc/passwd File first column .

    perform cat /etc/passwd command , You can view all the information in the specified file , We need to screen out root、bin、daemon The information in this column （ Here's the picture ）.

    awk Common options include ：

    ①-F “ Separator ” Indicates the field separator used for input , The default delimiter is several consecutive white space characters ;

    ②-v var=value Variable assignment

    Just these two options can be used in this exercise , First look -F Options . Because it is separated by colon ,-F Followed by ：（ Add it here or not “” Fine ）; The first column is filtered , The domain ID at the time of output is $1, The perform  awk -F: '{print $1}' /etc/passwd Command to get the first column （ Here's the picture ）.

    Look again. -v Options , Use -v Option , We can use awk Built in variables in FS（ Enter field separator , The default is blank , Function equivalent to -F）, That is, the variable is assigned FS=":", perform  awk -v FS=":" '{print $1}' /etc/passwd Can get /ettc/passwd File first column （ Here's the picture ）.