Shells, Scripting and Data Management practice questions

SHELL

Why wrong: SHELL is set by cron to /bin/sh or the user's shell.

LANG

Why wrong: LANG affects locale but not command availability.

HOME

Why wrong: HOME is set by cron to the user's home directory.

set -e

Why wrong: -e exits on error but does not print commands.

set -vx

Why wrong: -v prints shell input lines, but does not exit on error.

set -ux

Why wrong: -u treats unset variables as error, -x prints commands, but does not exit on command failure.

Equal to the number of lines in the file

Why wrong: The file has one line but multiple words.

Once

Why wrong: The loop iterates over each word, not the whole line.

The loop will not execute

Why wrong: The loop will execute for each word.

The cron job lacks the PATH environment variable.

Why wrong: The cron job specifies the full path to the script.

The script is owned by root, but the cron job runs as a different user.

Why wrong: Cron runs as root, matching the owner.

The script lacks a shebang line.

Why wrong: A shebang is not required for cron if the script is executable.

ps -ef | sort -k5,5 -rn

Why wrong: This is redundant and still sorts by the 5th field, but option D is more common.

ps -ef | sort -k3 -rn

Why wrong: -k3 is PID, not RSS.

ps --sort=rss

Why wrong: This sorts by RSS ascending, not descending.

sed 's/old/new/g' file.txt permanently changes the file.

Why wrong: Without -i, sed outputs to stdout, does not change the file.

sed uses extended regular expressions by default.

Why wrong: By default, sed uses basic regular expressions; -E enables extended.

The cron daemon is not running.

Why wrong: If cron daemon were not running, the job would not run at all.

The script requires a terminal to run.

Why wrong: Scripts can run without a terminal.

Cron automatically suppresses all output.

Why wrong: Cron does not suppress output; it attempts to email it.

The 'weekly' directive is misspelled.

Why wrong: 'weekly' is correctly spelled.

The /etc/logrotate.d/ directory is not included by logrotate.conf.

Why wrong: logrotate.conf includes /etc/logrotate.d/*.

The 'missingok' directive prevents rotation if the log file is missing, but the file exists.

Why wrong: 'missingok' is correct and does not prevent rotation.

trap 'echo error' ERR

Why wrong: Traps errors but does not prevent exit if set -e is active; also not the simplest method.

unset -e

Why wrong: unset -e is not a valid command; -e is not a variable.

set -e

Why wrong: This causes the script to exit on any error, opposite of desired.

# set +e

Why wrong: A comment does not affect shell behavior.

cat data.txt | wc -c

Why wrong: wc -c counts characters.

grep -c '.*' data.txt

Why wrong: grep -c counts matching lines; '.*' matches all lines but if file empty, count is 0; not standard.

sed -n '$=' data.txt

Why wrong: sed -n '$=' prints line number of last line, not count (same if file non-empty but fails for empty).

The script interpreter specified in the shebang is missing.

Why wrong: It's an ELF binary, not a script.

The library libc.so.6 is missing.

Why wrong: ldd shows it is present.

The file does not have execute permission for the user.

Why wrong: The file has execute permission for all.

grep -i 'ERROR' logfile

Why wrong: This case-insensitively matches lines containing ERROR.

grep -w 'ERROR' logfile

Why wrong: This matches whole words only, still showing lines containing ERROR.

grep 'ERROR' logfile

Why wrong: This shows lines containing ERROR.

${file##*/}

Why wrong: Removes the longest prefix matching */, yielding syslog.

${file%%/*}

Why wrong: Removes the longest suffix matching /*, yielding empty string.

${file#*/}

Why wrong: Removes the shortest prefix matching */, yielding /var/log/syslog.

The file has an empty line at the end.

Why wrong: Would not cause variable to be empty after loop.

The variable is declared as readonly.

Why wrong: Would cause an error, not just empty.

The variable name contains spaces.

Why wrong: Variable names cannot contain spaces.

sed 's/foo/bar/g' file

Why wrong: The g flag replaces all occurrences.

sed 's/foo/bar/0' file

Why wrong: Invalid flag 0; sed would error.

sed 's/foo/bar/2' file

Why wrong: Replaces the second occurrence per line.

awk -F: '{print $1,$2}' file

Why wrong: Prints name and age (second field).

awk -F: '{print $1 $3}' file

Why wrong: Concatenates fields without space.

awk -F: '{print $1 $2}' file

Why wrong: Concatenates name and age.

<< EOF

Why wrong: Unquoted delimiter allows variable expansion.

<<- EOF

Why wrong: Allows leading tabs and variable expansion.

<< "EOF"

Why wrong: Double quotes still allow variable expansion.

cat file | uniq | sort

Why wrong: uniq without prior sort removes only adjacent duplicates.

sort -u file

Why wrong: This works as well.

cat file | sort | uniq

Why wrong: This works but is not the only correct option.