[module]
name = "xargs"
description = "Build and execute command lines from standard input"
version = 1
[intro]
text = """
## What is xargs?
`xargs` reads items from standard input and executes a command with those items as arguments. It's the glue that connects the output of one command to the arguments of another.
## Basic Syntax
```
command | xargs [OPTIONS] [command]
```
## Common Options
- `-I {}` — replace `{}` with each input item
- `-0` — input items are null-terminated (pairs with `find -print0`)
- `-n N` — use at most N arguments per command invocation
- `-P N` — run up to N processes in parallel
- `-t` — print each command before executing it
## When to Use xargs
- `find . -name '*.log' | xargs rm` — delete found files
- `cat urls.txt | xargs curl -O` — download multiple URLs
- `find . -name '*.rs' | xargs grep 'TODO'` — search in found files
"""
[[examples]]
title = "Basic piping"
description = "Echo each word from a file as a separate argument"
command = "cat words.txt | xargs echo"
output = "apple banana cherry\n"
[[examples]]
title = "One argument at a time"
description = "Process each item individually with -n 1"
command = "cat words.txt | xargs -n 1 echo"
output = "apple\nbanana\ncherry\n"
[[examples]]
title = "Placeholder substitution"
description = "Use -I to place each item in a specific spot in the command"
command = "cat names.txt | xargs -I {} echo 'Hello, {}!'"
output = "Hello, Alice!\nHello, Bob!\n"
[[exercises]]
id = "xargs.1"
difficulty = "beginner"
question = """The file `files.txt` lists filenames, one per line.
Use xargs to pass them all to `echo` as a single invocation."""
expected_output = "a.txt b.txt c.txt\n"
hints = [
"Pipe cat files.txt into xargs echo",
"Try: cat files.txt | xargs echo",
]
solution = "cat files.txt | xargs echo"
match_mode = "exact"
[[exercises.fixtures]]
filename = "files.txt"
content = "a.txt\nb.txt\nc.txt\n"
[[exercises]]
id = "xargs.2"
difficulty = "beginner"
question = """The file `names.txt` has one name per line.
Use xargs to echo each name on its own line (one argument per invocation)."""
expected_output = "Alice\nBob\nCharlie\n"
hints = [
"Use -n 1 to pass one argument at a time",
"Try: cat names.txt | xargs -n 1 echo",
]
solution = "cat names.txt | xargs -n 1 echo"
match_mode = "exact"
[[exercises.fixtures]]
filename = "names.txt"
content = "Alice\nBob\nCharlie\n"
[[exercises]]
id = "xargs.3"
difficulty = "intermediate"
question = """The file `names.txt` has one name per line.
Use xargs with -I to print 'Hello, NAME!' for each name."""
expected_output = "Hello, Alice!\nHello, Bob!\nHello, Charlie!\n"
hints = [
"Use -I {} to define a placeholder",
"Try: cat names.txt | xargs -I {} echo 'Hello, {}!'",
]
solution = "cat names.txt | xargs -I {} echo 'Hello, {}!'"
match_mode = "exact"
[[exercises.fixtures]]
filename = "names.txt"
content = "Alice\nBob\nCharlie\n"
[[exercises]]
id = "xargs.4"
difficulty = "intermediate"
question = """Use find to locate all `.txt` files in the current tree, then use xargs to count the total lines across all of them with `wc -l`."""
expected_output = "5\n"
hints = [
"Pipe find output into xargs wc -l, then use tail or grep for the total",
"Try: find . -name '*.txt' | xargs wc -l | tail -1 | awk '{print $1}'",
]
solution = "find . -name '*.txt' | xargs wc -l | tail -1 | awk '{print $1}'"
match_mode = "exact"
[[exercises.fixtures]]
filename = "a.txt"
content = "one\ntwo\nthree\n"
[[exercises.fixtures]]
filename = "b.txt"
content = "four\nfive\n"
[[exercises]]
id = "xargs.5"
difficulty = "advanced"
question = """The file `targets.txt` lists directory names to create.
Use xargs to create all of them with mkdir."""
expected_output = "dir_a\ndir_b\ndir_c\n"
hints = [
"Use xargs mkdir to create directories from the list",
"Then use ls to verify: cat targets.txt | xargs mkdir && ls",
]
solution = "cat targets.txt | xargs mkdir && ls"
match_mode = "sorted"
[[exercises.fixtures]]
filename = "targets.txt"
content = "dir_a\ndir_b\ndir_c\n"
[[exercises]]
id = "xargs.6"
difficulty = "advanced"
question = """The file `paths.txt` has file paths with spaces in them.
Use null-delimited xargs (-0) after tr to handle the spaces safely, then echo each path."""
expected_output = "file one.txt\nfile two.txt\n"
hints = [
"Use tr '\\n' '\\0' to convert newlines to null bytes, then xargs -0",
"Try: cat paths.txt | tr '\\n' '\\0' | xargs -0 -n 1 echo",
]
solution = "cat paths.txt | tr '\\n' '\\0' | xargs -0 -n 1 echo"
match_mode = "exact"
[[exercises.fixtures]]
filename = "paths.txt"
content = "file one.txt\nfile two.txt\n"