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Top Forums UNIX for Dummies Questions & Answers Read the line from the last and display the one which is non-zero Post 302936089 by hariniiyer300 on Monday 23rd of February 2015 01:53:24 AM
Old 02-23-2015
Quote:
Originally Posted by Don Cragun
I am glad that you have code that does what you want. But, it does not do what you requested. You said that if the last line is 0, it should print the previous line. The previous line is the next to the last line of the file (which also contains 0; not ijhk which is the next to the next to the last line).

Code that seems to do what you requested, even though it is not what you apparently want, is:
Code:
tail -n 2 file | (
    read -r prev
    read -r last
    if [ "$last" = '0' ]
    then    printf '%s\n' "$prev"
    else    printf '%s\n' "$last"
    fi
)

or as a 1-liner:
Code:
tail -n2 file|(read -r prev;read -r last;[ "$last" = '0' ]&&printf '%s\n' "$prev"||printf '%s\n' "$last")

If your system has a really old version of the tail (and it doesn't support a -n option, change the:
Code:
tail -n2 file

in either script to:
Code:
tail -2 file

Note that either of these scripts will give you an empty line of output if your input file doesn't contain at least two lines. Your problem statement didn't say anything about what should happen if there are less than two lines in your input file.

Many thanks Mr. Don Cragun. My current requirement is if the line before the last line is also 0 , then I would want to print the line which has non -zero value in it. And as noted that that code might not work for less than 2 lines. But I will definitely have the first line loaded with value.

- Meenakshi
 

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TAIL(1) 						    BSD General Commands Manual 						   TAIL(1)

NAME
tail -- display the last part of a file SYNOPSIS
tail [-F | -f | -r] [-q] [-b number | -c number | -n number] [file ...] DESCRIPTION
The tail utility displays the contents of file or, by default, its standard input, to the standard output. The display begins at a byte, line or 512-byte block location in the input. Numbers having a leading plus ('+') sign are relative to the beginning of the input, for example, ``-c +2'' starts the display at the second byte of the input. Numbers having a leading minus ('-') sign or no explicit sign are relative to the end of the input, for example, ``-n 2'' displays the last two lines of the input. The default start- ing location is ``-n 10'', or the last 10 lines of the input. The options are as follows: -b number The location is number 512-byte blocks. -c number The location is number bytes. -f The -f option causes tail to not stop when end of file is reached, but rather to wait for additional data to be appended to the input. The -f option is ignored if the standard input is a pipe, but not if it is a FIFO. -F The -F option implies the -f option, but tail will also check to see if the file being followed has been renamed or rotated. The file is closed and reopened when tail detects that the filename being read from has a new inode number. The -F option is ignored if reading from standard input rather than a file. -n number The location is number lines. -q Suppresses printing of headers when multiple files are being examined. -r The -r option causes the input to be displayed in reverse order, by line. Additionally, this option changes the meaning of the -b, -c and -n options. When the -r option is specified, these options specify the number of bytes, lines or 512-byte blocks to display, instead of the bytes, lines or blocks from the beginning or end of the input from which to begin the display. The default for the -r option is to display all of the input. If more than a single file is specified, each file is preceded by a header consisting of the string ``==> XXX <=='' where XXX is the name of the file unless -q flag is specified. EXIT STATUS
The tail utility exits 0 on success, and >0 if an error occurs. SEE ALSO
cat(1), head(1), sed(1) STANDARDS
The tail utility is expected to be a superset of the IEEE Std 1003.2-1992 (``POSIX.2'') specification. In particular, the -F, -b and -r options are extensions to that standard. The historic command line syntax of tail is supported by this implementation. The only difference between this implementation and historic versions of tail, once the command line syntax translation has been done, is that the -b, -c and -n options modify the -r option, i.e., ``-r -c 4'' displays the last 4 characters of the last line of the input, while the historic tail (using the historic syntax ``-4cr'') would ignore the -c option and display the last 4 lines of the input. HISTORY
A tail command appeared in PWB UNIX. BSD
June 29, 2006 BSD
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