Convert a date string using perl

· jswank's blog

This procedure takes a data in the form YYYY-MM-DD and generates the epoch (UNIX) time using perl.

Procecdure #

1s/^(\d{4})-(\d{2})-(\d{2})$/timegm_posix(0,0,18,$3,$2-1,$1-1900)/e

Comments #

Use a regex with capture groups to isolate the year, month, and date, then substitute substitute the line with the scalar returned by timegm_posix(). The /e allows for the right side / replacement in the regex to be an expression rather than text.

Examples #

Run this script as a one-liner.

$ echo "1999-04-01" | \
  perl -MTime::Local=timegm_posix -pE 's/^(\d{4})-(\d{2})-(\d{2})$/timegm_posix(0,0,18,$3,$2-1,$1-1900)/e'

Comparing performance with a typical shell script.

Create a bunch of dates.

$ perl -E 'map { printf "%04d-%02d-%02d\n", (1992..2022)[rand 30], (1..12)[rand 12], (01..28)[rand 28] } 1..1000' \
  > dates.txt"

Create the shell script

$ cat epoch.sh << EOF
while read d; do date -d "${d} 18:00:00Z" done 
EOF

Time the execution

$ time bash epoch.sh < dates.txt >/dev/null
  0.79s user 0.31s system 103% cpu 1.066 total"

$ time perl epoch.pl dates.txt >/dev/null
  0.03s user 0.01s system 96% cpu 0.050 total"

See Also #

#perl #time