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Full Discussion: What does this command do?
Top Forums UNIX for Beginners Questions & Answers What does this command do? Post 302981334 by jlliagre on Saturday 10th of September 2016 09:22:32 AM
Old 09-10-2016
This function doing what its name and message states, it checks if the first column of the file passed as an argument contains sorted and unique values otherwise output an error message and exit in failure.

The function code could have been written a more pedagogical way but conciseness was preferred. Here is a more readable variant:

Code:
check_sorted_and_uniq() {
  if ! cmp  <(awk '{print $1}' $1 | sort | uniq) <(awk '{print $1}' $1); then
    echo "$0: file $1 is not in sorted order or has duplicates"
    exit 1;
  fi
}

The "<(...)" syntax creates a transient file that is passed to the program as an argument and which contains the result of the command being inside the parenthesis.

Note that "awk '{print $1}' $1" is simply outputting the first column of the file passed as first argument. "$1" has totally different meanings for awk and for the shell.
These 2 Users Gave Thanks to jlliagre For This Post:
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LEARN ABOUT ULTRIX

cmp

cmp(1)							      General Commands Manual							    cmp(1)

Name
       cmp - compare two files

Syntax
       cmp [-l | -s] file1 file2  [ skip1 ]  [ skip2 ]

Description
       The  command  compares two files.  If either file1 or file2 is `-', standard input is used for the file.  With no options, makes no comment
       if the files are the same.  If they differ, it reports the byte and line number at which the difference occurred to  standard  output.	If
       one file is an initial subsequence of the other a message including the file name is written to standard error.

       The optional skip1 and skip2 parameters are initial byte offsets into file1 and file2 respectively and may be either octal, by specifying a
       leading 0, or decimal.  When using skip1 and skip2 the offset is treated as the start of the respective input file.  Only one option may be
       specified  at  a  time.	Only one of the input files may be standard input at a time.  Because the line number is not calculated when using
       either of the options the use of either flag will increase the speed of

Options
       -l Long format:	prints the byte number (decimal) and the differing bytes (octal) for each difference.

       -s Suppresses normal output and sets the exit code only.

Diagnostics
       Exit code 0 is returned for identical files, 1 for different files, and 2 for an inaccessible or missing argument.

See Also
       comm(1), diff(1)

																	    cmp(1)
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