Use a Bash loop with append redirection:
for ((i=0; i<3; i++)); do
cat -- source.txt >> combined.txt
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Repeat one file a fixed number of times
The >> operator appends command output to a file and creates the destination if it does not exist. The Bash arithmetic for loop runs the cat command once per iteration.
for ((i=0; i<5; i++)); do
cat -- source.txt >> combined.txt
doneIn this example, the source contents are appended five times. The loop starts at zero and continues while i is less than five.
Build a fresh output file
Appending preserves anything already in the destination. If the result must contain only the new repetitions, truncate the destination once before starting the loop:
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: > combined.txt
for ((i=0; i<3; i++)); do
cat -- source.txt >> combined.txt
doneThe first command empties or creates combined.txt; each later command appends another copy. Do not put the truncation command inside the loop, or every iteration will erase the previous one.
Append several source files repeatedly
Give cat several operands when each repetition should contain the files in a specific order:
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for ((i=0; i<3; i++)); do
cat -- part1.txt part2.txt part3.txt >> combined.txt
doneEach pass appends part1.txt, then part2.txt, then part3.txt. To concatenate the files just once, omit the loop:
cat -- part1.txt part2.txt part3.txt >> combined.txtAppend generated command output
The same pattern works for any command that writes to standard output:
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for ((i=0; i<3; i++)); do
date >> combined.txt
doneEach iteration appends that command’s output. For a pipeline that must append to multiple files, GNU tee -a uses append mode:
some_command | tee -a first.log second.log > /dev/nullWithout -a, tee overwrites its destination files.
Append versus overwrite
| Syntax | Behavior | Use it when |
|---|---|---|
>> |
Appends to the existing destination; creates it when absent. | You must preserve existing content or add repeated output. |
> |
Truncates the destination before writing. | You intentionally want to replace the previous result. |
Because append mode does not clear the file, running the loop again adds another set of copies. Truncate the destination first only when a clean rebuild is intended.
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Avoid copying onto the input file
Never run a command such as:
cat -- source.txt > source.txtThe shell opens the output file before cat reads it and truncates the original, potentially destroying the input. The same hazard applies when an input path also appears as the destination in a larger concatenation command. Always use a separate output path, for example:
cat -- source.txt >> combined.txtChecks before running
- Confirm the repetition count is the number you actually want.
- Use
>>for accumulation and>only for deliberate replacement. - Ensure the destination is not one of the input files.
- Use
--before file names so a name beginning with a hyphen is treated as a file, not an option. - Remember that each run of an append loop adds more data to an existing destination.
When the count is supplied as a variable
Store the desired number in a variable when a script or user input determines it:
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count=3
: > combined.txt
for ((i=0; i<count; i++)); do
cat -- source.txt >> combined.txt
doneThis keeps the loop body unchanged while allowing the count to be adjusted in one place.
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