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Full Discussion: Check the exit status in a pipe call
Top Forums Shell Programming and Scripting Check the exit status in a pipe call Post 302561975 by Corona688 on Wednesday 5th of October 2011 04:04:49 PM
Old 10-05-2011
Quote:
Originally Posted by Rkolbe
As I said my app (an C app) have to be informed if the GZIP got any problem.
If your app doesn't have any idea where the info is supposed to end, that's a problem. if gzip dies instantly that's one thing, no data read, but if it dies halfway through? It doesn't get gzip's exit status and doesn't know gzip wasn't supposed to end there.

Your code could run its own gunzip instead, and would be able to get its exit status that way.

---------- Post updated at 02:04 PM ---------- Previous update was at 02:00 PM ----------

Something like:

Code:
$ cat popen.c
#include <stdio.h>
#include <sys/wait.h> // for wexitstatus
#include <sys/types.h>

int main(void)
{
        int status;
        char buf[512];
        FILE *fp=popen("gunzip", "r"); // Decompress, reading from stdin

        while(fgets(buf, 512, fp)) // Read until EOF
                printf("%s", buf);

        if(WEXITSTATUS(status=pclose(fp)))
                printf("gunzip failed with status %d, do rollback\n", WEXITSTATUS(status));
}
$ gcc popen.c
$ echo asdf | gzip | ./a.out
asdf
$ echo asdf | ./a.out

gzip: stdin: not in gzip format
gunzip failed with status 1, do rollback
$

This User Gave Thanks to Corona688 For This Post:
Rkolbe
 

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LEARN ABOUT NETBSD

gzcat

GZIP(1) 						    BSD General Commands Manual 						   GZIP(1)

NAME

     gzip -- compression/decompression tool using Lempel-Ziv coding (LZ77)

SYNOPSIS

     gzip [-cdfhlNnqrtVv] [-S suffix] file [file [...]]
     gunzip [-cfhNqrtVv] [-S suffix] file [file [...]]
     zcat [-fhV] file [file [...]]

DESCRIPTION

     The gzip program compresses and decompresses files using Lempel-Ziv coding (LZ77).  If no files are specified, gzip will compress from stan-
     dard input, or decompress to standard output.  When in compression mode, each file will be replaced with another file with the suffix, set by
     the -S suffix option, added, if possible.	In decompression mode, each file will be checked for existence, as will the file with the suffix
     added.

     If invoked as gunzip then the -d option is enabled.  If invoked as zcat or gzcat then both the -c and -d options are enabled.

     This version of gzip is also capable of decompressing files compressed using compress(1) or bzip2(1).

OPTIONS

     The following options are available:

     -1, --fast

     -2

     -3

     -4

     -5

     -6

     -7

     -8

     -9, --best        These options change the compression level used, with the -1 option being the fastest, with less compression, and the -9
		       option being the slowest, with optimal compression.  The default compression level is 6.

     -c, --stdout, --to-stdout
		       This option specifies that output will go to the standard output stream, leaving files intact.

     -d, --decompress, --uncompress
		       This option selects decompression rather than compression.

     -f, --force       This option turns on force mode.  This allows files with multiple links, overwriting of pre-existing files, reading from or
		       writing to a terminal, and when combined with the -c option, allowing non-compressed data to pass through unchanged.

     -h, --help        This option prints a usage summary and exits.

     -l, --list        This option displays information about the file's compressed and uncompressed size, ratio, uncompressed name.  With the -v
		       option, it also displays the compression method, CRC, date and time embedded in the file.

     -N, --name        This option causes the stored filename in the input file to be used as the output file.

     -n, --no-name     This option stops the filename and timestamp from being stored in the output file.

     -q, --quiet       With this option, no warnings or errors are printed.

     -r, --recursive   This option is used to gzip the files in a directory tree individually, using the fts(3) library.

     -S suffix, --suffix suffix
		       This option changes the default suffix from .gz to suffix.

     -t, --test        This option will test compressed files for integrity.

     -V, --version     This option prints the version of the gzip program.

     -v, --verbose     This option turns on verbose mode, which prints the compression ratio for each file compressed.

ENVIRONMENT

     If the environment variable GZIP is set, it is parsed as a white-space separated list of options handled before any options on the command
     line.  Options on the command line will override anything in GZIP.

SEE ALSO

     bzip2(1), compress(1), xz(1), fts(3), zlib(3)

HISTORY

     The gzip program was originally written by Jean-loup Gailly, licensed under the GNU Public Licence.  Matthew R. Green wrote a simple front
     end for NetBSD 1.3 distribution media, based on the freely re-distributable zlib library.	It was enhanced to be mostly feature-compatible
     with the original GNU gzip program for NetBSD 2.0.

     This manual documents NetBSD gzip version 20040427.

AUTHORS

     This implementation of gzip was written by Matthew R. Green <mrg@eterna.com.au>.

BSD
								   June 18, 2011							       BSD
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