If-then - Nested vs. blocks (Bash)
Versie door Jeroen Strompf (overleg | bijdragen) op 6 mrt 2023 om 21:04
I don't think this is a design pattern, but it's a small thing I've noticed over the years: When you need to check for multiple conditions, it's usually easier to do so in blocks of 'loosely coupled' statements, rather than in one 'tightly integrated' nested if-then statements: The latter is so much more work to understand and use.
The case that I use here, is about evaluating different ways that this routine gets its only argument: Against which website (within an Apache server) should it execute?
Nested statements
The promise of these nested statements is, that it is very efficient and somehow natural:
###############################################################################
# Initialisation
###############################################################################
#
# Welcome message
########################################
#
echo ""; echo ""; echo "### wp_sr_up.sh()..."
# 1. Process command line argument?
########################################
#
# * $0: Name of the script
# * $1: First argument, etc.
#
#
if
#
# Check if command line argument has been provided
#
[ "$1" ]
then
#
echo " Command line argument has been provided: $1"
#
# Check command line argument
########################################
#
if
[ -f "$1/wp-config.php" ]
then
#
echo " Command line argument seems to point to a valid WordPress site"
path_local="$1"
else
echo " File ${1}/wp-config.php not found. Exiting"
exit
fi
else
#
echo " Executed without command line argument..."
#
# 2. Executed from the root of a site?
########################################
#
if
[ -f "./wp-config.php" ]
then
echo " PWD seems to be the the root of a WordPress site"
path_local="$1"
else
#
echo " Executed outside the root of a WordPress site..."
#
# 3. Global variable "$path" being used?
########################################
#
# Does "$path" have content?
#
echo " Variable path: $path"
#
if
[ "$path" ]
then
echo " Variable 'path' contains value: $path"
#
# Check for wp-config.php
#
if
[ -f "$path/wp-config.php" ]
then
#
# $path seems valid. Ask user for confirmation
#
echo " Path seems ok"
read -p " Continue (y/n)? " continue
#
if
[ "$continue" = "y" ]
then
#
path_local="$1"
#
else
#
echo " Terminated by user"
exit
#
fi
else
#
echo " Variable 'path' has a value, but doesn't seem to point to a valid WordPress site"
echo " Exiting."
exit
#
fi
else
#
echo " Variable path doesn't seem to contain any value"
echo " Exiting."
exit
#
fi
fi
fi
Hybrid
In stead of nested if-then-statements, it is now in three blocks, which some of them still contain a nested statement:
###############################################################################
# Argument
###############################################################################
#
# Reset path_local
########################################
#
path_local=""
# 1. Command line argument?
########################################
#
# * $0: Name of the script
# * $1: First argument, etc.
#
if
[ "$1" ]
then
#
echo " Command line argument provided: $1"
#
if
[ -f "$1/wp-config.php" ]
then
#
echo " Command line argument seems to point to a valid WordPress site"
path_local="$1"
else
echo " File ${1}/wp-config.php not found. Exiting"
exit
fi
else
#
echo " No command line argument provided"
#
fi
# 2. PWD is a WordPress site?
########################################
#
if
[[ ! "$path_local" ]] && [ -f "./wp-config.php" ]
then
#
echo " PWD seems to be a WordPress site."
#
path_local="$1"
#
else
#
echo " PWD doesn't seem to be a WordPress site."
#
fi
# 3. Global variable "$path" being used?
########################################
#
if
[[ ! "$path_local" ]] && [ "$path" ]
then
#
echo " Global variable 'path' seems to have a value"
#
if
[ -f "$path/wp-config.php" ]
then
#
# $path seems valid. Ask user for confirmation
#
echo " Path seems ok"
read -p " Continue (y/n)? " continue
#
if
[ "$continue" = "y" ]
then
#
path_local="$1"
#
else
#
echo " Terminated by user"
exit
#
fi
else
#
echo " Variable 'path' has a value, but doesn't seem to point to a valid WordPress site"
echo " Exiting."
exit
#
fi
else
#
echo " Variable path doesn't seem to contain any value"
echo " Exiting."
exit
#
fi
Only blocks
Now without any nested if-then-statements (except for the third case, where user input is incorporated):
- Not every case is tested (and reported about by using
echo, but it's much easier to read and to maintain - I think that's way more important - To my surprise, this is only 82 lines of code, compaired to 104 for the first example (which also reported much more extensively)
- BTW, I only now found some errors in the previous scripts.
###############################################################################
# Argument
###############################################################################
#
# Reset path_local
########################################
#
path_local=""
# 1. Command line argument?
########################################
#
# * $0: Name of the script
# * $1: First argument, etc.
#
if
[ "$1" ] && [ -f "$1/wp-config.php" ]
then
#
echo " Command line argument provided: $1"
echo " Command line argument seems to point to a valid WordPress site"
path_local="$1"
#
fi
# 2. PWD is a WordPress site?
########################################
#
if
[[ ! "$path_local" ]] && [ -f "./wp-config.php" ]
then
#
echo " PWD seems to be a WordPress site."
path_local="$PWD"
#
fi
# 3. Global variable "$path" being used?
########################################
#
if
[[ ! "$path_local" ]] && [ "$path" ] && [ -f "$path/wp-config.php" ]
then
#
echo " Global variable 'path' seems to point to a WordPress site"
read -p " Continue (y/n)? " continue
#
if
[ "$continue" = "y" ]
then
#
path_local="$path"
#
else
#
echo " Terminated by user"
#
fi
#
fi
# Still no value? → Exit
########################################
#
if
[[ ! "$path_local" ]]
then
#
echo " No WordPress site found. Exiting"
exit
#
fi
# Got a value!
########################################
#
echo " And the path is: $path_local"