The following bash script fulfills your requirements:

#!/usr/bin/env bash

if (($# == 0)) || [[ "$1" == "--help" ]] || [[ "$1" == "-h" ]]; then
  echo "Usage: $0 <filename> [<filename> ...]"
  exit 1
fi

echo "Passphrase:"
stty -echo
IFS="" read -r passphrase
stty echo

for arg in "$@"; do
  gpg --batch --symmetric --passphrase-fd 0 --cipher-algo AES256 "$arg" <<< "$passphrase"
done

• Save it as enc.sh and make it executable with chmod +x enc.sh.
• To encrypt multiple files, execute ./enc.sh file1 file2 ... and enter your passphrase which is required once.
• Files are encrypted with GnuPG using AES-256.
• The passphrase will not be leaked through the terminal, the shell history or /proc's cmdline.
• To decrypt a file execute gpg filename.gpg or use gpg --multifile --decrypt file1.gpg file2.gpg ... to decrypt multiple files at once.

The following bash script fulfills your requirements:

#!/usr/bin/env bash

# Print usage information of the script
if (($# == 0)) || [[ "$1" == "--help" ]] || [[ "$1" == "-h" ]]; then
  echo "Usage: $0 <filename> [<filename> ...]"
  exit 1
fi

echo "Passphrase:"
# Disable output to prevent terminal leakage of passphrase when the passphrase is entered
stty -echo
# Read passphrase via standard input
# The "-r" parameter of read prevents the interpretation of escape sequences
# Setting the IFS (Internal Field Separator) environment variable empty to allow the passphrase to contain whitespaces
IFS="" read -r passphrase
# Enable output
stty echo 

# Execute GnuPG to encrypt every file with AES-256 given as a parameter to the script
for arg in "$@"; do
  gpg --batch --symmetric --passphrase-fd 0 --cipher-algo AES256 "$arg" <<< "$passphrase"
done

• Save it as enc.sh and make it executable with chmod +x enc.sh.
• To encrypt multiple files, execute ./enc.sh file1 file2 ... and enter your passphrase which is required once.
• Files are encrypted with GnuPG using AES-256.
• The passphrase will not be leaked through the terminal, the shell history or /proc's cmdline.
• To decrypt a file execute gpg filename.gpg or use gpg --multifile --decrypt file1.gpg file2.gpg ... to decrypt multiple files at once.