Debugging Scripts

PS4 Prefix

Shape Trace Lines

PS4 controls the prefix Bash uses for execution traces. Modeling the prefix helps explain set -x output without printing noisy traces.

Program

Play the script to choose a trace prefix and build one modeled trace line.

ps4_prefix.sh 
#!/usr/bin/env bash

prefix=
command="echo ready"
trace_line="${prefix}${command}"
echo "$trace_line"

#!/usr/bin/env bash

prefix=
command="echo ready"
trace_line="${prefix}${command}"
echo "$trace_line"
PS4 `PS4` is the prompt prefix Bash prints before traced commands.
set -x `set -x` emits commands as Bash expands and runs them.
modeled trace This example prints one trace-shaped line instead of enabling global tracing.