An absolute path starts at the root / and works from anywhere; a relative path starts from wherever you currently are.

* Standing in labstudent, the same file is reached by an absolute path from / or a relative path through ... *

The single giveaway is the leading slash. If a path begins with /, the shell reads it from the top of the tree — unambiguous, location-independent. If it doesn't, the shell silently glues it onto your current directory, so the same text means different files depending on where you're standing.

Three special references make relative paths powerful:

• . — the current directory
• .. — the parent directory (one level up)
• ~ — your home directory

Same target, two ways, standing in /home/labstudent:

cat /home/labadmin/file   # absolute: works from anywhere
cat ../labadmin/file      # relative: go up to /home, then into labadmin

When to use which: reach for absolute paths in scripts and config files, where you can't predict the working directory and a wrong guess is a bug. Reach for relative paths when typing interactively near your target — they're shorter and faster. The trade-off is robustness vs. brevity.

Strings use symbol operators: = (equal), != (not equal), plus -z (empty) and -n (non-empty).

Note the split-brain design: strings use =/!=, numbers use -eq/-ne. Mixing them is a common bug — [ "$a" -eq "$b" ] errors if the values aren't integers. The -z/-n checks are invaluable for validating input: -z "$var" is true when the variable is empty or unset, perfect for "did the user pass an argument?"

Examples:

name="admin"

if [ "$name" = "admin" ]; then
    echo "Welcome admin"
fi

if [ -z "$name" ]; then
    echo "Name is empty"
fi

if [ -n "$name" ]; then
    echo "Name is set: $name"
fi

Always quote variables:

# Correct
[ "$var" = "value" ]

# WRONG - breaks if var is empty
[ $var = "value" ]     # Becomes [ = "value" ] - syntax error!