tex-which, phaoMath blog, https://phaomath.blogspot.com/

#!/bin/bash

function tex_search (
  TEX_PKGS_DIR=/usr/share/texlive/texmf-dist/tex/

  echo -n Looking for \\$1 in $TEX_PKGS_DIR ...

  # This amount of needed \\ is because we're doing escapes for bash strings and also for grep.
  results_fname=$(mktemp)
  find $TEX_PKGS_DIR -type f \( -iname '*.tex' -or -iname '*.sty' -or -iname '*.cls' \) -exec grep -Ei "(command|cmd|new|def|decl)[^\\\\]*\\\\$1[^a-zA-Z]" '{}' + | grep "\\\\$1[^a-zA-Z]" > $results_fname

  echo ' (done)'
  echo
  echo Found possible symbol definition for \\$1 in files:

  # read -r makes it treat backslash not as an escape character, but as part of the string.
  cat $results_fname | while read -r occur
  do
    basename $(echo $occur | cut -d ':' -f 1)
  done | sort -u | tr '\n' '\t' | fmt

  echo
  echo Full results:

  cat $results_fname | while read -r occur
  do
    full_path=$(echo $occur | cut -d ':' -f 1)
    code=$(echo $occur | cut -d ':' -f 2)
    full_dir=$(dirname $full_path)
    dir=${full_dir#*$TEX_PKGS_DIR}
    echo $(basename $full_path) in $dir
    echo -en "\t"
    echo $code | tr -d '\n' | grep -i "\\\\$1" --color=always
  done

  rm $results_fname
)

# The option -R in less is so that it handle colors well.
tex_search "$1" | less -R