I'm looping over a series of large files with a shell script:
i=0
while read line
do
# get first char of line
first=`echo "$line" | head -c 1`
# make output filename
name="$first"
if [ "$first" = "," ]; then
name='comma'
fi
if [ "$first" = "." ]; then
name='period'
fi
# save line to new file
echo "$line" >> "$2/$name.txt"
# show live counter and inc
echo -en "\rLines:\t$i"
((i++))
done <$file
The first character in each line will either be alphanumeric, or one of the above defined characters (which is why I'm renaming them for use in the output file name).
It's way too slow.
5,000 lines takes 128seconds.
At this rate I've got a solid month of processing.
Will awk be faster here?
If so, how do I fit the logic into awk?
This can certainly be done more efficiently in bash.
To give you an example: echo foo | head
echo foo | head
does a fork()
call, creates a subshell, sets up a pipeline, starts the external head
program... and there's no reason for it at all.
If you want the first character of a line, without any inefficient mucking with subprocesses, it's as simple as this:
c=${line:0:1}
I would also seriously consider sorting your input, so you can only re-open the output file when a new first character is seen, rather than every time through the loop.
That is -- preprocess with sort (as by replacing <$file
with < <(sort "$file")
) and do the following each time through the loop, reopening the output file only conditionally:
if [[ $name != "$current_name" ]] ; then
current_name="$name"
exec 4>>"$2/$name" # open the output file on FD 4
fi
...and then append to the open file descriptor:
printf '%s\n' "$line" >&4
(not using echo because it can behave undesirably if your line is, say, -e
or -n
).
Alternately, if the number of possible output files is small, you can just open them all on different FDs up-front (substituting other, higher numbers where I chose 4
), and conditionally output to one of those pre-opened files. Opening and closing files is expensive -- each close()
forces a flush to disk -- so this should be a substantial help.
#!/usr/bin/awk -f
BEGIN {
punctlist = ", . ? ! - '"
pnamelist = "comma period question_mark exclamation_mark hyphen apostrophe"
pcount = split(punctlist, puncts)
ncount = split(pnamelist, pnames)
if (pcount != ncount) {print "error: counts don't match, pcount:", pcount, "ncount:", ncount; exit}
for (i = 1; i <= pcount; i++) {
punct_lookup[puncts[i]] = pnames[i]
}
}
{
print > punct_lookup[substr($0, 1, 1)] ".txt"
printf "\r%6d", i++
}
END {
printf "\n"
}
The BEGIN
block builds an associative array so you can do punct_lookup[","]
and get "comma".
The main block simply does the lookups for the filenames and outputs the line to the file. In AWK, >
truncates the file the first time and appends subsequently. If you have existing files that you don't want truncated, then change it to >>
(but don't use >>
otherwise).
A few things to speed it up:
Don't use echo/head to get the first character. You're spawning at least two additional processes per line. Instead, use bash's parameter expansion facilities to get the first character.
Use if-elif to avoid checking $first
against all the possibilities each time. Even better, if you are using bash 4.0 or later, use an associative array to store the output file names, rather than checking against $first
in a big if-statement for each line.
If you don't have a version of bash that supports associative arrays, replace your if statements with the following.
if [[ "$first" = "," ]]; then name='comma' elif [[ "$first" = "." ]]; then name='period' else name="$first" fi
But the following is suggested. Note the use of $REPLY
as the default variable used by read
if no name is given (just FYI).
declare -A OUTPUT_FNAMES
output[","]=comma
output["."]=period
output["?"]=question_mark
output["!"]=exclamation_mark
output["-"]=hyphen
output["'"]=apostrophe
i=0
while read
do
# get first char of line
first=${REPLY:0:1}
# make output filename
name=${output[$first]:-$first}
# save line to new file
echo $REPLY >> "$name.txt"
# show live counter and inc
echo -en "\r$i"
((i++))
done <$file
Yet another take:
declare -i i=0
declare -A names
while read line; do
first=${line:0:1}
if [[ -z ${names[$first]} ]]; then
case $first in
,) names[$first]="$2/comma.txt" ;;
.) names[$first]="$2/period.txt" ;;
*) names[$first]="$2/$first.txt" ;;
esac
fi
printf "%s\n" "$line" >> "${names[$first]}"
printf "\rLine $((++i))"
done < "$file"
and
awk -v dir="$2" '
{
first = substr($0,1,1)
if (! (first in names)) {
if (first == ",") names[first] = dir "/comma.txt"
else if (first == ".") names[first] = dir "/period.txt"
else names[first] = dir "/" first ".txt"
}
print > names[first]
printf("\rLine %d", NR)
}
'
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