Linux (49)


Sort on nth field

To sort a text file on a particular field: [code] Sort -t: -k 4n thefile [/code] So thefile will be output, sorted by the 4th field.

Read more...



watch mysql queries as they happen

cunning bit of Perl, not to be used permanently, but very handy indeed for a quick look at what’s actually being queried… [code] tcpdump -i eth0 -s 0 -l -w – dst port 3306 | strings | perl -e ‘ while(<>) { chomp; next if /^[^ ]+[ ]*$/; if(/^(SELECT|UPDATE|DELETE|INSERT|SET|COMMIT|ROLLBACK|CREATE|DROP|ALTER)/i) { if (defined $q) { print […]

Read more...



remove blank lines in vi

  • September 1, 2012
  • vi

to remove blank lines in vi: [code]:v/\S/d [/code]

Read more...



Checking variables

  • August 30, 2012
  • Linux

test if a variable is empty [code][ "$var" ] || echo ‘it be empty'[/code] or check if $var is not null using -n: [code] if [ -n "$var" ]; then # its not null fi [/code] or check if $var is not empty using -ne: [code] if [ -ne "$var" ]; then # its not […]

Read more...



Changing ownership of files to another user

  • August 30, 2012
  • Linux

Change the ownership of multiple files and directories to a different user: [code]$ find /the/path/ -user olduser -group olduser -exec chown newuser:newgroup {} \;[/code]

Read more...



Must be root

  • August 30, 2012
  • Linux

A check to see if the user is root. Useful for scripts that must be run as root. [code] # check for root if [ $(id -u) != "0" ]; then echo "no" exit 0 fi echo "ok…" # start the script… [/code]

Read more...



Recover .swp file in vi

  • August 29, 2012
  • vi

I was just editing a file in vi on my iPad using diet coda. Hadn’t saved it and the app crashed. Boo. Tried to open the .swp file, oops, don’t do that. Instead, use: [code]vi -r file[/code] Open the file as if it existed, but using the -r flag (recover, suprisingly) vi will look for […]

Read more...



count a unique field in text file

i was just perusing my access_log, and fancied counting the number of times unique ip addresses had access my site. just because. i started by using cat to see the access_log cut the first field using cut -f1 -d’ ‘ sorted that list of ip’s uniq’d it and used -c to add a count then […]

Read more...



line numbers in vi and goto line in vi

  • August 28, 2012
  • vi

There are some by handy shortcuts in vi, to say the least, it’s a very comprehensive program. So here is how to turn on line numbers in vi and how to goto line in vi. To turn line numbers on, do [code]:set number[/code] To jump to a specific line, a colon followed by the number […]

Read more...