Technomancy

While poking around I discovered that you can use the stty size command to get the dimensions in columns and rows of the current terminal window.

This little bash functions can help. We have to tell stty what terminal (ie tty) to use. By default it’ll use the stdin, which doesn’t work if you’re chaining commands.

TTY=$(tty)
function rows {
    stty --file=${TTY} size | sed 's/^([0-9]*) ([0-9]*)/1/'
}
function cols {
    stty --file=${TTY} size | sed 's/^([0-9]*) ([0-9]*)/2/'
}

Example usage:

dmesg | tail -n $(( $(rows) - 2 ))

I am currently uploading some files to a remote computer, however my internet connection is not great. The connection intermittantly dies, killing the upload. I have to restart the upload as soon as I notice this. Luckily I’m using rsync, so files aren’t uploaded again.

I don’t want to have to restart the command. This little script, ‘do-till-done’ will repeatidly execute a command until it ends successfully (i.e. an exit status of 0). It used the libnotify notification system for GNOME to alert you when it needs to rerun a command. It waits 1 seconds between failures. Pressing Control-C will stop that iteration of the programme. To stop it fully, press Control-C while it’s in the sleep phase. i.e. press Control-C twice quickly.

Script:

#! /bin/bash

PROGNAME=$(basename $0)

COMMAND=$*

$COMMAND

while [ $? -ne 0 ] ;
do
    notify-send --urgency=low "${PROGNAME}" "${COMMAND} failed${WAIT_STR}"

    sleep 1

    $COMMAND
done

notify-send --urgency=normal "${PROGNAME}" "${COMMAND} finished"

This programme is in the public domain.

Sample usage:

$ do-till-done rsync -aPh *.jpg example.org:public_html/photos/

Shell scripts usually operate on a line by line basis, i.e. each line is a separate field. However MySQL uses “field1″,”field2″,.. type groups (e.g. for “SELECT * FROM table WHERE field IN ( “field1″,”field2″,.. );” ). This little alias will join all those lines together into something copy/pasteable into a MySQL query.

alias 'quotejoin=sed -e "s/^/"/" -e "s/$/",/" | tr -d "n" | sed "s/,$/n/"'

Example use:

$ cat test
line1
line2
line3
$ cat test | quotejoin
"line1","line2","line3"
$

Sometimes when testing programmes that call other programmes, it’s important to be able to see what was called and what was on the stdin. This script prints all that info back to you.

#! /bin/bash
echo "script: args: $*"
while read line; do
    echo "script: stdin: $line"
done

exit 0

Example use:

$ cat > foo
Hello
this is line 2
$ cat foo | ./echor arg1 -n arg3
script: args: arg1 -n arg3
script: stdin: Hello
script: stdin: this is line 2

A lot of scripting languages like perl or python have good string and regular expression (regex) support. By using grep, you can have this in bash. Normally grep prints out the lines that match the regex. But with the -q option, it doesn’t print anything and exits as soon as it finds a match (or gets to the end). The return code will be 0 if it wasn’t found, or non-zero if it was found. This is ideal for including in an if clause. Remember to include ‘^’ and ‘$’ to ensure the regex is the only input.

eg:

if echo $VAR | grep -q '^d{3,10}$' ; then
  echo "VAR matches"
fi

Turns out you can do this in bash already but only in bash 3.0 or above.

gnome-terminal is the default terminal for GNOME. It is a tabbed terminal emulator. You can change the title of the current tab with this command, which will change the title to “TITLE”.

echo -en "33]0;TITLEa"

This function will do that for you, just put it in your ~/.bashrc

function title {
    echo -en "33]0;$*a"
}

Use it like this:

$ title foo

EDIT Sun 10th June 2007: You can now have spaces in your tab title