Expansion and Data

Quoting

Words vs One Value

Quoting controls how Bash splits text into command arguments. The same variable can become two words or one value.

Program

Play the script to see unquoted text split on a space, then quoted text stay together.

quoting.sh
Replay: real traced execution (multi-file project)
#!/usr/bin/env bash

item="daily report"
printf '<%s>\n' $item
printf '<%s>\n' "$item"

  1. item ← daily report

    3item="daily report"4printf '<%s>\n' $item
    values this stepdaily reportitem

  2. printf '<%s> ' $item

    3item="daily report"4printf '<%s>\n' $item5printf '<%s>\n' "$item"
    output<daily>
<report>
    values this stepdaily reportitemdaily, reportwords

  3. printf '<%s> ' "$item"

    4printf '<%s>\n' $item5printf '<%s>\n' "$item"
    output<daily report>
    values this stepdaily reportitemdaily reportwords

Follow the Words

  1. item starts as daily report.
  2. The unquoted $item is split on the space.
  3. The first printf receives two arguments: daily and report.
  4. The quoted "$item" stays as one argument.
  5. The second printf prints one line: <daily report>. | run | argument flow | output | | --- | --- | --- | | unquoted | daily report -> daily, report | <daily>, then <report> | | quoted | daily report stays one value | <daily report> |
word splitting After unquoted expansion, Bash splits text into words using whitespace.
double quotes Double quotes preserve spaces while still allowing variable expansion.

Exercise: quoting.sh

Reproduce the two unquoted lines and the one quoted line, then change item to another two-word value and predict the printed lines.