Finding first appearance of text in Mercurial repository

try hg grep Example *.php

hg grep [OPTION]... PATTERN [FILE]...

search for a pattern in specified files and revisions

    Search revisions of files for a regular expression.

    This command behaves differently than Unix grep. It only
    accepts Python/Perl regexps. It searches repository
    history, not the working directory. It always prints the
    revision number in which a match appears.

    By default, grep only prints output for the first
    revision of a file in which it finds a match. To get it
    to print every revision that contains a change in match
    status ("-" for a match that becomes a non-match, or "+"
    for a non-match that becomes a match), use the --all
    flag.

options:

 -0 --print0              end fields with NUL
    --all                 print all revisions that match
 -f --follow              follow changeset history, or file
                          history across copies and renames
 -i --ignore-case         ignore case when matching
 -l --files-with-matches  print only filenames and revisions
                          that match
 -n --line-number         print matching line numbers
 -r --rev                 search in given revision range
 -u --user                list the author (long with -v)
 -d --date                list the date (short with -q)
 -I --include             include names matching the given
                          patterns
 -X --exclude             exclude names matching the given
                          patterns

use "hg -v help grep" to show global options

The selected answer is incomplete:

hg grep --all --files-with-matches 'PATTERN' [FILES]

is normally what you want.