I can use herestrings to pass a string to a command, e.g.
cat <<< "This is a string"
How can I use herestrings to pass two strings to a command? How can I do something like
### not working
diff <<< "string1" "string2"
### working but overkill
echo "string1" > file1
echo "string2" > file2
diff file1 file2
You can't use two herestrings as input to the same command. In effect, the latest one will replace all others. Demonstration:
cat <<< "string 1" <<< "string 2" <<< "string 3"
# only shows "string 3"
On the other hand, if what you want is really diff two immediate inputs, you can do it this way:
diff <(echo "string 1") <(echo "string 2")
< and (?
< and (, follow @gniourf_gniourf's link (+1). It could be said it's just defined this way, like you can't put a space in the middle of a [[ or of a <<<. There's probably an actual ambiguity-resolving reason behind as well.echo construct passes strings as command-line parameters; process substitution (the <() construct) is a bit more involved but ends up providing a file name as a command-line parameter. All those construct fit the definition of “passing strings to commands”, so your question was pretty ambiguous. (comment rewritten because of the huge mistake that haunted its previous version)You can simply concatenate the two strings:
cat <<< "string1""string2"
(not the lack of space between the two). The here string now consists of a single word whose contents are the contents of the two strings.
diff?diff <( echo "string1" ) <( echo "string2" )will work.diffstrings? Why not[ "$string1" = "$string2" ] && echo equal || echo "not equal"?diff <<< "string 1" "string 2"is parsed as a call todiffwith a single command-line argument"string 2"and standard input bound to a"string 1"-seeding stream. It expects two command-line arguments, sees only one, and stops there, not consuming the standard input. You could actually get it to work by comparing to standard input:diff - file2 <<< "string 1"