continue - Linux
Overview
The continue command is used within looping constructs in shell scripts in Linux. Its primary function is to skip the remaining commands in the current loop iteration and proceed with the next iteration of the loop. This command is most effective in scenarios where certain conditions might require prematurely skipping to the next cycle of a loop without terminating the loop entirely.
Syntax
The basic syntax of the continue
command is as follows:
continue [n]
Where [n]
is an optional argument specifying the number of nesting levels of loops to skip. If [n]
is not provided, it defaults to 1, which affects the immediate loop.
Options/Flags
The continue
command does not have any options or flags. The only parameter it takes is an optional numeric argument [n]
, which allows control over multiple nested loops.
- [n]: An integer specifying the number of loop levels to continue past. If omitted, it defaults to 1, affecting the current loop.
Examples
-
Simple Continue
In a basic for loop, skip numbers that are divisible by 3:for i in {1..10}; do if (( i % 3 == 0 )); then continue fi echo $i done
This will output numbers from 1 to 10 excluding multiples of 3.
-
Nested Loop Continue
Usingcontinue
with a level argument in nested loops:for i in {1..3}; do for j in {1..3}; do if (( i == j )); then continue 2 fi echo "i=$i, j=$j" done done
This script skips the output for pairs where
i
equalsj
.
Common Issues
-
Misunderstanding Loop Levels: A common error occurs when users specify an incorrect level number for nested loops. This can either cause the script to behave unexpectedly or result in a syntax error.
Solution: Ensure the correct nesting level number is used and thoroughly test in complex loop scenarios.
-
Relying on
continue
Outside Loops: Ifcontinue
is mistakenly placed outside of any loop, it will cause a scripting error.Solution: Review that
continue
is only used within the intended loop constructs.
Integration
The continue
command can be combined with other Linux commands in scripts to facilitate more complex decision-making and loop control. Here’s an example integrating continue
with grep
:
for filename in *.txt; do
grep -q 'error' "$filename"
if [ $? -eq 0 ]; then
continue
fi
echo "Processing $filename"
done
This script checks for the presence of the word “error” in .txt
files, skipping files that contain the term.
Related Commands
break
: Used to exit from loop constructs.for
,while
,until
: Commands to create loop constructs which can be controlled bycontinue
.
For a deeper understanding of shell scripting and loop controls, visiting the Bash manual page (man bash
) or online resources like the GNU Bash Reference Manual can be beneficial.