[SOLVED] -z and -Z in grep

Issue

I paste grep manual on arguments -z and -Z.

   -z, --null-data
          Treat input and output data as sequences of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline.  Like the -Z  or  --null
          option, this option can be used with commands like sort -z to process arbitrary file names.

   -Z, --null
          Output a zero byte (the ASCII NUL character) instead of the character that normally follows a file name.  For example, grep -lZ outputs a zero byte  after
          each  file  name instead of the usual newline.  This option makes the output unambiguous, even in the presence of file names containing unusual characters
          like newlines.  This option can be used with commands like find -print0, perl -0, sort -z, and xargs -0 to process arbitrary file names, even  those  that
          contain newline characters.

Create a test file:

vim  "/tmp/target/it is a test.txt"
test

For -Z ,it output a zero byte 00 at the end of file.

grep -rlZ  'test' /tmp/target |xxd
00000000: 2f74 6d70 2f74 6172 6765 742f 6974 2069  /tmp/target/it i
00000010: 7320 6120 7465 7374 2e74 7874 00         s a test.txt.

For -z,it Treat input and output data as sequences of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline..

grep -rlz  'test' /tmp/target |xxd
00000000: 2f74 6d70 2f74 6172 6765 742f 6974 2069  /tmp/target/it i
00000010: 7320 6120 7465 7374 2e74 7874 0a         s a test.txt.

Why -z add 0a instead of 00?What does output mean in Treat input and output data as sequences of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline.?

Solution

Why -z add 0a instead of 00?What does output mean in Treat input and output data as sequences of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline.?

The -z option is about the data that grep is matching against the given pattern. It has two effects:

1. The data will be interpreted as having null-terminated lines instead of newline-terminated lines.

2. When grep echos input data to its output (normally a line matching the pattern, but if -v is in effect then a line not matching the pattern) then it terminates that line with a null character, thus preserving that characteristic of the input. This is what "output" means in the documentation for the -z option.

Neither of those is relevant to your particular data and grep -rlz command.

In the first place, the contents of file /tmp/target/it is a test.txt is just test -- no null characters in sight. grep therefore treats the entire contents of the file as one line, though that's no different than if -z were not in effect, there being no newline either.

In the second place, the -l option is in effect, so instead of printing any matched lines (with null terminators), grep prints the name of the file. It appends a newline because that is its default, and you have not overridden it -- filename printing is what the -Z option is about, not the -z option.

Note also that -Z is effective on filename printing even when -l is not in effect. When -r is in effect or multiple filenames are given on the grep command line, grep will normally precede each line of input data it prints (that is, each output line) with the corresponding file name and a colon. When -Z is in effect, it instead precedes each line with the file name and a null character.

Answered By - John Bollinger

Answer Checked By - Katrina (WPSolving Volunteer)