how to align lines to the left side with sed or perl one line liner

Question

we have the following file

how alignment lines to the left side with sed or perl one line liner

more conf.env

# Extra ssh options.  Empty by default.
    export HADOOP_SSH_OPTS="-o ConnectTimeout=5 -o SendEnv=HADOOP_CONF_DIR"

# Where log files are stored.  $HADOOP_HOME/logs by default.
  export HADOOP_LOG_DIR={{hdfs_log_dir_prefix}}/$USER

# History server logs
               export HADOOP_MAPRED_LOG_DIR={{mapred_log_dir_prefix}}/$USER

# Where log files are stored in the secure data environment.
         export HADOOP_SECURE_DN_LOG_DIR={{hdfs_log_dir_prefix}}/$HADOOP_SECURE_DN_USER

   # File naming remote slave hosts.  $HADOOP_HOME/conf/slaves by default.
# export HADOOP_SLAVES=${HADOOP_HOME}/conf/slaves

expected results

more conf.env

# Extra ssh options.  Empty by default.
export HADOOP_SSH_OPTS="-o ConnectTimeout=5 -o SendEnv=HADOOP_CONF_DIR"

# Where log files are stored.  $HADOOP_HOME/logs by default.
export HADOOP_LOG_DIR={{hdfs_log_dir_prefix}}/$USER

# History server logs
export HADOOP_MAPRED_LOG_DIR={{mapred_log_dir_prefix}}/$USER

# Where log files are stored in the secure data environment.
export HADOOP_SECURE_DN_LOG_DIR={{hdfs_log_dir_prefix}}/$HADOOP_SECURE_DN_USER

# File naming remote slave hosts.  $HADOOP_HOME/conf/slaves by default.
# export HADOOP_SLAVES=${HADOOP_HOME}/conf/slaves

Answer 1

This will delete all spaces and tabs at the beginning of every line:

sed 's/^[ \t]*//'

where

• ^ matches the beginning of a line
• [ \t] matches a space or a tab
• * makes the previous […] block work zero or more times, as many times as it can (so it can match multiple spaces and/or tabs)

The whole s/…// command replaces … pattern (^[ \t]* in this case) with nothing.

Example use:

sed 's/^[ \t]*//' <input.txt >output.txt

or in place (note -i is not required by POSIX):

sed -i 's/^[ \t]*//' file.txt