Alex's Unix hint's

This page is dedicated certain one-liners or scripts which I created during my work with various Unix-like enviroments and I considered worth remembering.
I'll try to categorize this as soon as it becomes neccessary.

  1. The missing option for "wc" - linelength

    2. When you import fixed column sized textfiles into a database you need to verify the file has no additional linebreaks, or to put it simple - you need to make sure all lines are complete and have the same length.
    I usually use this: 
    perl -n -e 'print length . "\n"' file
    This prints out each line's length, one number per line, so you can pipe this through sort and uniq (-c) to immediately see if something's wrong.
    But how to find out which of my 1 million lines is too short?
    You could pipe the output of above through "cat -n" to preceed each line with its linenumber and then grep for the deviating linelength. This would give you the linenumber, if you want to see the line you could then "cat -n file|grep linenumber" or use this 
    perl -n -e 'print length . ":$_"' file
    and grep for your linelength. This command prepends the length and a ':' to each line.
    If you just want to look at line X you can use: 
    sed -n Xp file
    Note that there is no space between the linenumber and "p". The last line would be '$' and the selection can be inverted by a '!' sign. So to print the whole file except for the last line do: 
    sed -n '$!p' file

    If your file is tab separated, you can use this to get the columns per line: 
    perl -n -e '@t=split("\t");print $#t . "\n"' file

  2. Remove old files

    3. If I want to automatically remove old files, I usually use something like this: 
    find /my/dir -type d -name log.\* -mtime +7 -print0|xargs -0 -r rm -Rf
    Nowadays you usually have newsyslog for taiming the logfiles, but this can be used for various purposes.

  3. Sorting files by version number

    4. To sort files by version numbers I once devised this contraption: 
    echo -e "foobar-2.0.0.tar.gz\nfoobar-1.4.1.tar.gz\nfoobar-1.3.21.tar.gz\nfoobar-1.3.9.tar.gz" | \
perl -ne 'push @t,$_;END{print sort{@a=split/(\D)/,$a;@ab=(@a);@b=split/(\D)/,$b;
@bb=(@b);my$t=0;while(shift(@a)eq shift(@b)){$t++;}if(($ab[$t]=~/\d+/)&&($bb[$t]=~/\d+/)){
$ab[$t]<=>$bb[$t];}else{$ab[$t]cmp$bb[$t];};}@t}'
    gives: 
    foobar-1.3.9.tar.gz
foobar-1.3.21.tar.gz
foobar-1.4.1.tar.gz
foobar-2.0.0.tar.gz
    I know it's not pretty but this is not as trivial as it sounds even some humans get confused..

  4. Missing "gdk-pixbuf.loaders" file?

    5. /usr/X11R6/bin/gdk-pixbuf-query-loaders >gdk-pixbuf.loaders
    should take care of that. Typical locations are:

  5. Verifying file integrity with public key crypto using openssl

    1. Create a new private key: 
      openssl genrsa -des3 -out mykey.pem 2048
    2. Create the public key: 
      openssl rsa -in mykey.pem -pubout >mykey.pub
    3. Create signature of your file "foo.sh" 
      openssl dgst -sha1 -sign mykey.pem -out foo.sh.sha1 foo.sh
    4. Verify signature for your file "foo.sh" 
      openssl dgst -sha1 -verify mykey.pub -signature foo.sh.sha1 foo.sh
      should give: 
      Verified OK