-n作用
[ -n 字符串 ] or [ 字符串 ] 字符串的长度为非零（有内容）则为真。加-n与不加-n结果相同。
-z作用
[ -z 字符串 ] 字符串的长度为零则为真。 字符串为空即NULL时为真，与上面的-n相反。
-f作用
[ -f FILE ] 如果 FILE 存在且是一个普通文件则为真。
ros系统环境为ros2 foxy。
系统自带的包source的第一个系统脚本文件
/opt/ros/foxy/setup.bash
bash
# copied from ament_package/template/prefix_level/setup.bash
AMENT_SHELL=bash
# source setup.sh from same directory as this file
AMENT_CURRENT_PREFIX=$(builtin cd "`dirname "${BASH_SOURCE[0]}"`" && pwd)
# trace output
if [ -n "$AMENT_TRACE_SETUP_FILES" ]; then
echo "# . \"$AMENT_CURRENT_PREFIX/setup.sh\""
fi
. "$AMENT_CURRENT_PREFIX/setup.sh"通过在终端显示这个变量验证，$AMENT_TRACE_SETUP_FILES没有内容。
[ -n "$AMENT_TRACE_SETUP_FILES" ]没有内容，if fi内代码不运行，直接跳到最后一句执行
bash
. "$AMENT_CURRENT_PREFIX/setup.sh"这个脚本文件的意思是运行同一个文件夹内的setup.sh文件，转入运行下面的脚本。
/opt/ros/foxy/setup.sh
bash
# generated from ament_package/template/prefix_level/setup.sh.in
# since this file is sourced use either the provided AMENT_CURRENT_PREFIX
# or fall back to the destination set at configure time
: ${AMENT_CURRENT_PREFIX:=/opt/ros/foxy}
# set type of shell if not already set
: ${AMENT_SHELL:=sh}
# function to append non-duplicate values to environment variables
# using colons as separators and avoiding leading separators
ament_append_unique_value() {
# arguments
_listname=$1
_value=$2
#echo "listname $_listname"
#eval echo "list value \$$_listname"
#echo "value $_value"
# check if the list contains the value
eval _values=\$$_listname
_duplicate=
_ament_append_unique_value_IFS=$IFS
IFS=":"
if [ "$AMENT_SHELL" = "zsh" ]; then
ament_zsh_to_array _values
fi
for _item in $_values; do
# ignore empty strings
if [ -z "$_item" ]; then
continue
fi
if [ $_item = $_value ]; then
_duplicate=1
fi
done
unset _item
# append only non-duplicates
if [ -z "$_duplicate" ]; then
# avoid leading separator
if [ -z "$_values" ]; then
eval $_listname=\"$_value\"
#eval echo "set list \$$_listname"
else
# field separator must not be a colon
unset IFS
eval $_listname=\"\$$_listname:$_value\"
#eval echo "append list \$$_listname"
fi
fi
IFS=$_ament_append_unique_value_IFS
unset _ament_append_unique_value_IFS
unset _duplicate
unset _values
unset _value
unset _listname
}
# iterate over all parent_prefix_path files
_prefix_setup_IFS=$IFS
IFS="
"
# this variable contains the concatenated prefix paths in reverse order
_UNIQUE_PREFIX_PATH=""
# this check is used to skip parent prefix path in the Debian package
if [ -z "SKIP_PARENT_PREFIX_PATH" ]; then
# find parent prefix path files for all packages under the current prefix
_RESOURCES="$(\find "$AMENT_CURRENT_PREFIX/share/ament_index/resource_index/parent_prefix_path" -mindepth 1 -maxdepth 1 2> /dev/null | \sort)"
if [ "$AMENT_SHELL" = "zsh" ]; then
ament_zsh_to_array _RESOURCES
fi
for _resource in $_RESOURCES; do
# read the content of the parent_prefix_path file
_PARENT_PREFIX_PATH="$(\cat "$_resource")"
# reverse the list
_REVERSED_PARENT_PREFIX_PATH=""
IFS=":"
if [ "$AMENT_SHELL" = "zsh" ]; then
ament_zsh_to_array _PARENT_PREFIX_PATH
fi
for _path in $_PARENT_PREFIX_PATH; do
# replace placeholder of current prefix
if [ "$_path" = "{prefix}" ]; then
_path="$AMENT_CURRENT_PREFIX"
fi
# avoid leading separator
if [ -z "$_REVERSED_PARENT_PREFIX_PATH" ]; then
_REVERSED_PARENT_PREFIX_PATH=$_path
else
_REVERSED_PARENT_PREFIX_PATH=$_path:$_REVERSED_PARENT_PREFIX_PATH
fi
done
unset _PARENT_PREFIX_PATH
# collect all unique parent prefix path
if [ "$AMENT_SHELL" = "zsh" ]; then
ament_zsh_to_array _REVERSED_PARENT_PREFIX_PATH
fi
for _path in $_REVERSED_PARENT_PREFIX_PATH; do
ament_append_unique_value _UNIQUE_PREFIX_PATH "$_path"
done
unset _REVERSED_PARENT_PREFIX_PATH
done
unset _resource
unset _RESOURCES
fi
# append this directory to the prefix path
ament_append_unique_value _UNIQUE_PREFIX_PATH "$AMENT_CURRENT_PREFIX"
unset AMENT_CURRENT_PREFIX
# store AMENT_SHELL to restore it after each prefix
_prefix_setup_AMENT_SHELL=$AMENT_SHELL
# source local_setup.EXT or local_setup.sh file for each prefix path
IFS=":"
if [ "$AMENT_SHELL" = "zsh" ]; then
ament_zsh_to_array _UNIQUE_PREFIX_PATH
fi
for _path in $_UNIQUE_PREFIX_PATH; do
# trace output
if [ -n "$AMENT_TRACE_SETUP_FILES" ]; then
echo "# . \"$_path/local_setup.$AMENT_SHELL\""
fi
if [ -f "$_path/local_setup.$AMENT_SHELL" ]; then
if [ "$AMENT_SHELL" = "sh" ]; then
# provide AMENT_CURRENT_PREFIX to .sh files
AMENT_CURRENT_PREFIX=$_path
fi
# restore IFS before sourcing other files
IFS=$_prefix_setup_IFS
. "$_path/local_setup.$AMENT_SHELL"
# restore AMENT_SHELL after each prefix-level local_setup file
AMENT_SHELL=$_prefix_setup_AMENT_SHELL
fi
done
unset _path
IFS=$_prefix_setup_IFS
unset _prefix_setup_IFS
unset _prefix_setup_AMENT_SHELL
unset _UNIQUE_PREFIX_PATH
unset AMENT_SHELL我们自己生成的包source环境变量脚本
工作空间内 source install/setup.bash
bash
# generated from colcon_bash/shell/template/prefix_chain.bash.em
# This script extends the environment with the environment of other prefix
# paths which were sourced when this file was generated as well as all packages
# contained in this prefix path.
# function to source another script with conditional trace output
# first argument: the path of the script
_colcon_prefix_chain_bash_source_script() {
if [ -f "$1" ]; then
if [ -n "$COLCON_TRACE" ]; then
echo ". \"$1\""
fi
. "$1"
else
echo "not found: \"$1\"" 1>&2
fi
}
# source chained prefixes
# setting COLCON_CURRENT_PREFIX avoids determining the prefix in the sourced script
COLCON_CURRENT_PREFIX="/opt/ros/foxy"
_colcon_prefix_chain_bash_source_script "$COLCON_CURRENT_PREFIX/local_setup.bash"
# source this prefix
# setting COLCON_CURRENT_PREFIX avoids determining the prefix in the sourced script
COLCON_CURRENT_PREFIX="$(builtin cd "`dirname "${BASH_SOURCE[0]}"`" > /dev/null && pwd)"
_colcon_prefix_chain_bash_source_script "$COLCON_CURRENT_PREFIX/local_setup.bash"
unset COLCON_CURRENT_PREFIX
unset _colcon_prefix_chain_bash_source_script$0当前脚本名 $1 脚本的第一个参数
_colcon_prefix_chain_bash_source_script(){}函数的意思是第一个参数文件存在就运行第一个参数，没有就报错。
所以我们在自己的工作空间source install/setup.bash相当于同时source /opt/ros/foxy/local_setup.bash
source install/local_setup.bash