Using sed to find, convert and replace lines - bash

Question

I don't know too much of bash scripting and I'm trying to develop a bash script to do this operations:
I have a lot of .txt files in the same directory.
Every .txt file follows this structure:
file1.txt:
<name>first operation</name>
<operation>21</operation>
<StartTime>1292435633</StartTime>
<EndTime>1292435640</EndTime>
<name>second operation</name>
<operation>21</operation>
<StartTime>1292435646</StartTime>
<EndTime>1292435650</EndTime>
I want to search every <StartTime> line and convert it to standard date/time format (not unix timestamp) but preserving the structure <StartTime>2010-12-15 22:52</StartTime>, for example. This could be a function of search/replace, using sed? I think I could use these function that I found: date --utc --date "1970-01-01 $1 sec" "+%Y-%m-%d %T"
I want to to do the same with <EndTime> tag.
I should do this for all *.txt files in a directory.
I tried using sed but with not wanted results. As I said I don't know so much of bash scripting so any help would be appreciated.
Thank you for your help!
Regards

Answer 1

sed is incapable of doing date conversions; instead I would reccomend you to use a more appropriate tool like awk:
echo '<StartTime>1292435633</StartTime>' | awk '{
match($0,/[0-9]+/);
t = strftime("%F %T",substr($0,RSTART,RLENGTH),1);
sub(/[0-9]+/,t)
}
{print}'
If your input files have one tag per line, as in your structure example, it should work flawlessly.
If you need to repeat the operation for every .txt file just use a shell for:
for file in *.txt; do
awk '/^<[^>]*Time>/{
match($0,/[0-9]+/);
t = strftime("%F %T",substr($0,RSTART,RLENGTH),1);
sub(/[0-9]+/,t)
} 1' "$file" >"$file.new"
# mv "$file.new" "$file"
done
In comparison to the previous code, I have done two minor changes:
added condition /^<[^>]*Time>/ that checks if the current line starts with or
converted {print} to the shorter '1'
If the files ending with .new contain the result you were expecting, you can uncomment the line containing mv.

Answer 2

Using grep:
while read line;do
if [[ $line == *"<StartTime>"* || $line == *"<EndTime>"* ]];then
n=$(echo $line | grep -Po '(?<=(>)).*(?=<)')
line=${line/$n/$(date -d #$n)}
fi
echo $line >> file1.new.txt
done < file1.txt
$ cat file1.new.txt
<name>first operation</name>
<operation>21</operation>
<StartTime>Wed Dec 15 18:53:53 CET 2010</StartTime>
<EndTime>Wed Dec 15 18:54:00 CET 2010</EndTime>
<name>second operation</name>
<operation>21</operation>
<StartTime>Wed Dec 15 18:54:06 CET 2010</StartTime>
<EndTime>Wed Dec 15 18:54:10 CET 2010</EndTime>