#!/bin/sh

# Edit a file without changing its timestamps.

# Both access and modification times are maintained,

# or optionally those timestamps are set to a specific epoch.

# License: LGPLv2

# Author:

# http://www.pixelbeat.org/

# Notes:

# $EDITOR if set, must not fork at startup, so if you

# want to use gvim for example, ensure EDITOR="gvim -f".

# Currently linux can read timestamps with nanosecond resolution

# but only set a specific timestamp with microsecond resolution

# (if the filesystem even supports that).

# Changes:

# V1.0, 31 May 2006, Initial release

# V1.1, 13 Jul 2007, Allow specifying epoch

# Remove the use of temp files

# V1.2, 24 Jul 2007, Fallback to second resolution for touch implementations

# that don't handle nanoseconds in the date string.

# Warn if nanosecond resolution is lost due to limitations

# in `touch`, the libc/kernel interface or the filesystem.

# V1.3, 05 Feb 2009, Don't allow to specify epoch with leading + or -

# as it's common to call vim like: vim file +line_num etc.

# Only allow 2 parameters rather than ignoring extra ones.

file="$1"

epoch="$2"

if [ ! -f "$file" ] || [ $# -ne 1 -a $# -ne 2 ]; then

echo "Usage: `basename $0` file [epoch]" >&2

exit 1

fi

if [ ! "$epoch" ]; then

epoch=`date --reference="$file" +%s.%N` || exit 1

else

if echo "$epoch" | grep -Eq "^[\+-]"; then

echo "Epochs with leading +/- are ambiguous with editor options" >&2

exit 1

fi

if ! date --date="1970-01-01 UTC $epoch seconds" >/dev/null 2>&1; then

echo "Invalid epoch specified [$epoch]" >&2

exit 1

fi

fi

if echo "$epoch" | grep -Fq "."; then #valid nanosecond format

seconds=`echo $epoch | cut -d. -f1`

if echo $epoch | grep -Eq "\.0+$"; then #strip redundant nanoseconds

epoch=$seconds #since touch may not support nanosecond format

else

checkns="true" #need to check nanosecond portion later

fi

fi

${EDITOR:-vim} "$file"

[ ! "$seconds" ] && err="/dev/tty" || err="/dev/null"

touch "$file" --date="1970-01-01 UTC $epoch seconds" 2>$err

if [ $? -ne 0 -a "$seconds" ]; then #maybe touch doesn't support nanoseconds

touch "$file" --date="1970-01-01 UTC $seconds seconds" &&

echo "Warning: sub second portion of timestamp ignored" >&2

else

if [ "$checkns" ]; then

new_ts=`date --reference="$file" +%s.%N`

diff=`echo "(($epoch-$new_ts)*10^9)/1" | bc`

if [ $diff -ne 0 ]; then

echo "Warning: timestamp set ${diff}ns backwards" >&2

fi

fi

fi

#Hmm could have option to inc time by 1 second

#so that updates would be noticed as normal

#but the relative ordering of a file in time

#in relation to other files would probably be unchanged