Commands by postrational (5)

  • Use this BASH trick to create a variable containing the TAB character and pass it as the argument to sort, join, cut and other commands which don't understand the \t notation. sort -t $'\t' ... join -t $'\t' ... cut -d $'\t' ... Show Sample Output


    5
    sort -t $'\t' -k 2 input.txt
    postrational · 2010-07-11 12:58:51 0
  • There is a common command for outputting a field or list of fields from each line in a file. Why wouldn't you just use cut?


    4
    cut -f 1 three-column.txt > first-column.txt
    postrational · 2010-07-11 10:13:45 1
  • Performs a reverse DNS lookup, variants include: nslookup 74.125.45.100 or: host 74.125.45.100 Show Sample Output


    4
    dig -x 74.125.45.100
    postrational · 2009-09-28 15:13:34 0
  • Date-time format: YYYY-MM-DD HH:MM:SS Show Sample Output


    7
    export HISTTIMEFORMAT='%F %T '
    postrational · 2009-09-26 17:13:23 0
  • Checks the Gmail ATOM feed for your account, parses it and outputs a list of unread messages. For some reason sed gets stuck on OS X, so here's a Perl version for the Mac: curl -u username:password --silent "https://mail.google.com/mail/feed/atom" | tr -d '\n' | awk -F '<entry>' '{for (i=2; i<=NF; i++) {print $i}}' | perl -pe 's/^<title>(.*)<\/title>.*<name>(.*)<\/name>.*$/$2 - $1/' If you want to see the name of the last person, who added a message to the conversation, change the greediness of the operators like this: curl -u username:password --silent "https://mail.google.com/mail/feed/atom" | tr -d '\n' | awk -F '<entry>' '{for (i=2; i<=NF; i++) {print $i}}' | perl -pe 's/^<title>(.*)<\/title>.*?<name>(.*?)<\/name>.*$/$2 - $1/' Show Sample Output


    46
    curl -u username:password --silent "https://mail.google.com/mail/feed/atom" | tr -d '\n' | awk -F '<entry>' '{for (i=2; i<=NF; i++) {print $i}}' | sed -n "s/<title>\(.*\)<\/title.*name>\(.*\)<\/name>.*/\2 - \1/p"
    postrational · 2009-09-07 21:56:40 6

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Use tee to process a pipe with two or more processes
Tee can be used to split a pipe into multiple streams for one or more process to work it. You can add more " >()" for even more fun.

open a seperate konsole tab and ssh to each of N servers (konsole 4.2+)
creates a new tab for each of N servers in listofservers.txt and ssh's to said servers then, try the "send to all sessions" feature of konsole to do the same work on all servers at the same time. BIG time saver, but be careful!

delay: a simple scheduler
the "delay" utility is an invaluable tool for me. with gnu-screen it allows you to schedule something and have it run and output to the current terminal, unlike "at". You can also use it like "sleep" with seconds and also with date: delay until 13:33 friday && echo test get it from: http://onegeek.org/~tom/software/delay/current/delay.c (author: Tom Rothamel)

Check if a command is available in your system
Usefull to detect if a commad that your script relies upon is properly installed in your box, you can use it as a function function is_program_installed() { type "$1" >/dev/null } Invoke it and check the execution code is_program_installed "dialog" if [ ! $? -eq 0 ]; then echo "dialog is not installed" exit 1 fi

Print info about your real user.
To get your effective user: whoami

Compress files in a directory

Delete more than one month old thumbnails from home directory
By time thumbnail images in ~/thumbnails take up too much space, this command will help deleting old ones. Find options explained: -type f : find files only, not directories -atime +30 : last accessed more than 30 days ago

Create a file of a given size in linux
if the fs support sparse file,using truncate can create sparse file. http://en.wikipedia.org/wiki/Sparse_file

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }


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