September 2008 Archives - Thoughts of a geek

Searching for shell builtins to speedup Nanoblogger, we stumbled across a very charming and nice way to implement a tail function in the Kornshell.

This works in KSH93 and newer.

The new redirection operators, <# and ># are used to seek. For example,

<# (( EOF-36 ))

will seek to 36 bytes before the end-of-file. You can apply this along with any redirection so that

cat < file <# (( 80 ))

will cat the file starting from offset 80. The value of $(n<#) is the current offset on file descriptor n.

The current syntax can be extended to add other seek options like SEEK_HOLE, by using,

<# (( HOLE ))

to seek to the next hole.

The new kernel for the EeePC (2.6.25) has deprecated the /proc/acpi/battery interface, so I had to write a new script for use in my zsh prompt.

The script will work in both 2.6.24 and 2.6.25, so without further ado, here it is. It is written as a function for easy inclusion in any prompts.

#!/bin/zsh
bat() {
PROC=/proc/acpi/battery/BAT0
SYS=/sys/class/power_supply/BAT0/uevent
STATE=
# dc: design capacity, rc: remaining capacity
if [ -f $PROC/info ]; then
    STATE=$PROC/state   # 2.6.24
    dc=$(grep 'last full' < $PROC/info | awk '{ print $4 }')
    rc=$(grep 'remaining' < $PROC/state | awk '{ print $3 }')
elif [ -f $SYS ]; then
    STATE=$SYS          # 2.6.25
    dc=$(grep '\<POWER_SUPPLY_CHARGE_FULL\>' < $SYS | awk -F= '{ print $2 }')
    rc=$(grep '\<POWER_SUPPLY_CHARGE_NOW\>' < $SYS | awk -F= '{ print $2 } ')
else
    exit
fi
p=$(echo 3k $rc $dc / 100 \* p | dc )

if grep -iq discharging $STATE; then
    printf " %02d" "$p"
else
    if [ ${p%.*} -lt 100 ]; then
    printf " %02d+" "$p"
    fi
fi
}
bat

Update

After some tweaking I even made a better one which saves a few greps.

#!/bin/zsh
bat() {
PROC=/proc/acpi/battery/BAT0
SYS=/sys/class/power_supply/BAT0/uevent
STATE=
# dc: design capacity, rc: remaining capacity
if [ -f $PROC/info ]
then
    STATE=$PROC/state   # 2.6.24
    dc=$(awk '/last full/ { print $4 }' $PROC/info)
    rc=$(awk '/remaining/ { print $3 }' $PROC/state)
elif [ -f $SYS ]
then
    STATE=$SYS          # 2.6.25
    dc=$(awk -F= '$1 ~ /^POWER_SUPPLY_CHARGE_FULL$/ { print $2 }' $SYS)
    rc=$(awk -F= '$1 ~ /^POWER_SUPPLY_CHARGE_NOW$/  { print $2 }' $SYS)
else
    return 0
fi

p=$(echo 3k $rc $dc / 100 \* p | dc )

if grep -iq discharging $STATE; then
    printf " %02d" "$p"
else
    if [ ${p%.*} -lt 100 ]; then
    printf " %02d+" "$p"
    fi
fi
}
bat

Update 2

Just found that there is also a nice tool, called acpi...which makes it even more easy:

% acpi -V
Battery 0: Full, 100%
AC Adapter 0: on-line
Thermal 0: ok, 53.0 degrees C
Cooling 0: Processor 0 of 7