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

    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?

    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 or: host Show Sample Output

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

    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 "" | 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 "" | 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

    curl -u username:password --silent "" | 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 12

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Add temporary swap space
In addition to a swap partition, Linux can also use a swap file. Some programs, like g++, can use huge amounts of virtual memory, requiring the temporary creation of extra space.

Create the oauth token required for a Twitter stream feed
This is the THIRD in a set of five commands. See my other commands for the previous two. This step creates the oauth 1.0 token as explained in The token is required for a Twitter filtered stream feed (and almost all Twitter API calls) This token is simply an encrypted version of your base string. The encryption key used is your hmac. The last part of the command scans the Base64 token string for '+', '/', and '=' characters and converts them to percentage-hex escape codes. (URI-escapeing). This is also a good example of where the $() syntax of Bash command substitution fails, while the backtick form ` works - the right parenthesis in the case statement causes a syntax error if you try to use the $() syntax here. See my previous two commands step1 and step2 to see how the base string variable $b and hmac variable $hmac are generated.

Find usb device in realtime
Using this command you can track a moment when usb device was attached.

escape any command aliases
e.g. if rm is aliased for 'rm -i', you can escape the alias by prepending a backslash: rm [file] # WILL prompt for confirmation per the alias \rm [file] # will NOT prompt for confirmation per the default behavior of the command

Recursive grep of all c++ source under the current directory
I like this better than some of the alternatives using -exec, because if I want to change the string, it's right there at the end of the command line. That means less editing effort and more time to drink coffee.

Netcat & Tar
Create a tarball on the client and send it across the network with netcat on port 1234 where its extracted on the server in the current directory.

pip install into current directory without virtualenv
For subsequent commands in the prefixed path: $ PYTHONPATH=$PWD/lib/python*/site-packages ./bin/pip --version

Exclude inserting a table from a sql import
Starting with a large MySQL dump file (*.sql) remove any lines that have inserts for the specified table. Sometimes one or two tables are very large and uneeded, eg. log tables. To exclude multiple tables you can get fancy with sed, or just run the command again on subsequently generated files.

Given a file path, unplug the USB device on which the file is located (the file must be on an USB device !)
You have an external USB drive or key. Apply this command (using the file path of anything on your device) and it will simulate the unplug of this device. If you just want the port, just type : echo $(sudo lshw -businfo | grep -B 1 -m 1 $(df "/path/to/file" | tail -1 | awk '{print $1}' | cut -c 6-8) | head -n 1 | awk '{print $1}' | cut -c 5- | tr ":" "-")

Create a mirror of a local folder, on a remote server
Create a exact mirror of the local folder "/root/files", on remote server 'remote_server' using SSH command (listening on port 22) (all files & folders on destination server/folder will be deleted)

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